fix: update timezone plugin to support custom parse format
fix #1159
**Describe the bug**
How to get the correct time stamp with a time on a specific timezone ?
I want to check the unix timestamp for 10/15/2020 12:30 PM at Denver, but neither of the approaches (3 and 4) works.

1.
//Los Angeles (correct)
console.log("local notz:", dayjs("10/15/2020 12:30 PM").unix().toString());
// local notz:1602790200
2.
//Los Angeles (wrong)
console.log("local:", dayjs.tz("10/15/2020 12:30 PM").unix().toString()); 
// local: 1602815400 
3.
// Denver (wrong)
console.log(
  "denver:",
  dayjs.tz("10/15/2020 12:30 PM", "America/Denver").unix().toString()
); 
//denver: 1602811800 
4.
// Denver (wrong)
console.log(
  "denver sep:",
  dayjs("10/15/2020 12:30 PM").tz("America/Denver").unix().toString()
); 
//denver sep: 1602790200 

**Expected behavior**
A clear and concise description of what you expected to happen.

1.1602790200
2.1602790200
3.1602793800
4.1602793800


**Information**
 - Day.js Version [e.g. v1.9.3]
 - OS: [e.g. macOS 10.15.7]
 - Browser [e.g. chrome 86]
 - Time zone: [e.g. GMT-07:00 DST (Pacific Daylight Time)]

the unix timestamp didnt not pick up the timezone change correctly
diff --git a/src/plugin/timezone/index.js b/src/plugin/timezone/index.js
index 06dd27c1f..593a3a6eb 100644
--- a/src/plugin/timezone/index.js
+++ b/src/plugin/timezone/index.js
@@ -114,14 +114,16 @@ export default (o, c, d) => {
     return result && result.value
   }
 
-  d.tz = function (input, timezone = defaultTimezone) {
+  d.tz = function (input, arg1, arg2) {
+    const parseFormat = arg2 && arg1
+    const timezone = arg2 || arg1 || defaultTimezone
     const previousOffset = tzOffset(+d(), timezone)
     let localTs
     if (typeof input !== 'string') {
       // timestamp number || js Date || Day.js
       localTs = d(input) + (previousOffset * 60 * 1000)
     }
-    localTs = localTs || d.utc(input).valueOf()
+    localTs = localTs || d.utc(input, parseFormat).valueOf()
     const [targetTs, targetOffset] = fixOffset(localTs, previousOffset, timezone)
     const ins = d(targetTs).utcOffset(targetOffset)
     ins.$x.$timezone = timezone
diff --git a/types/plugin/timezone.d.ts b/types/plugin/timezone.d.ts
index 491f87465..f356a8788 100644
--- a/types/plugin/timezone.d.ts
+++ b/types/plugin/timezone.d.ts
@@ -10,6 +10,7 @@ declare module 'dayjs' {
 
   interface DayjsTimezone {
     (date: ConfigType, timezone?: string): Dayjs
+    (date: ConfigType, format: string, timezone?: string): Dayjs
     guess(): string
     setDefault(timezone?: string): void
   }

diff --git a/test/plugin/timezone.test.js b/test/plugin/timezone.test.js
index 1f733baf6..59eb83111 100644
--- a/test/plugin/timezone.test.js
+++ b/test/plugin/timezone.test.js
@@ -2,10 +2,12 @@ import MockDate from 'mockdate'
 import moment from 'moment-timezone'
 import dayjs from '../../src'
 import timezone from '../../src/plugin/timezone'
+import customParseFormat from '../../src/plugin/customParseFormat'
 import utc from '../../src/plugin/utc'
 
 dayjs.extend(utc)
 dayjs.extend(timezone)
+dayjs.extend(customParseFormat)
 
 beforeEach(() => {
   MockDate.set(new Date())
@@ -17,6 +19,7 @@ afterEach(() => {
 
 const NY = 'America/New_York'
 const VAN = 'America/Vancouver'
+const DEN = 'America/Denver'
 const TOKYO = 'Asia/Tokyo'
 
 describe('Guess', () => {
@@ -281,3 +284,13 @@ describe('Get offsetName', () => {
     expect(d).toBe('Eastern Standard Time')
   })
 })
+
+describe('CustomPraseFormat', () => {
+  const result = 1602786600
+  it('normal', () => {
+    expect(dayjs.tz('2020/10/15 12:30', DEN).unix()).toBe(result)
+  })
+  it('custom', () => {
+    expect(dayjs.tz('10/15/2020 12:30', 'MM/DD/YYYY HH:mm', DEN).unix()).toBe(result)
+  })
+})

{"test/plugin/timezone.test.js": {"run": "PASS", "test": "FAIL", "fix": "PASS"}}
{"test/timezone.test.js:Add Time days (DST)": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/de.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/sk.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/advancedFormat.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/weekYear.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/timezone.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isSameOrBefore.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/pluralGetSet.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/timezone.test.js:Diff (DST)": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/keys.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/utils.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/relativeTime.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/parse.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/localizedFormat.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/updateLocale.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/constructor.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/weekday.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isLeapYear.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/query.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/localeData.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/zh.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/declarations.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/ru.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/dayOfYear.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/timezone.test.js:UTC add day in DST": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/manipulate.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/cs.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/en.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/get-set.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/utc.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/quarterOfYear.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/objectSupport.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/fi.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/sv.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/toArray.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/timezone.test.js:Utc Offset": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/utc-utcOffset.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/sr-cyrl.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/br.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isMoment.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isYesterday.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/pl.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/toObject.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/sr.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isSameOrAfter.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/weekOfYear.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/comparison.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/et.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/calendar.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isTomorrow.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/hu.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/timezone.test.js:UTC and utcOffset": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/arraySupport.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isToday.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/hr.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/badMutable.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/customParseFormat.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/duration.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isoWeek.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/minMax.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isoWeeksInYear.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/buddhistEra.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/uk.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/display.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/lt.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/zh-cn.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isBetween.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}}
{"test/plugin/timezone.test.js": {"run": "PASS", "test": "FAIL", "fix": "PASS"}}
{"passed_count": 70, "failed_count": 0, "skipped_count": 0, "passed_tests": ["test/timezone.test.js:Add Time days (DST)", "test/plugin.test.js", "test/locale/de.test.js", "test/get-set.test.js", "test/plugin/utc.test.js", "test/plugin/quarterOfYear.test.js", "test/plugin/objectSupport.test.js", "test/locale/fi.test.js", "test/locale/sk.test.js", "test/locale/sv.test.js", "test/plugin/advancedFormat.test.js", "test/plugin/weekYear.test.js", "test/plugin/toArray.test.js", "test/timezone.test.js", "test/timezone.test.js:Utc Offset", "test/plugin/isSameOrBefore.test.js", "test/plugin/pluralGetSet.test.js", "test/timezone.test.js:Diff (DST)", "test/plugin/utc-utcOffset.test.js", "test/locale/sr-cyrl.test.js", "test/utils.test.js", "test/locale/br.test.js", "test/plugin/relativeTime.test.js", "test/parse.test.js", "test/locale/keys.test.js", "test/plugin/isMoment.test.js", "test/plugin/isYesterday.test.js", "test/locale/pl.test.js", "test/plugin/toObject.test.js", "test/locale/sr.test.js", "test/plugin/localizedFormat.test.js", "test/plugin/updateLocale.test.js", "test/constructor.test.js", "test/plugin/weekday.test.js", "test/plugin/isSameOrAfter.test.js", "test/plugin/weekOfYear.test.js", "test/comparison.test.js", "test/plugin/isLeapYear.test.js", "test/query.test.js", "test/plugin/localeData.test.js", "test/locale/et.test.js", "test/plugin/calendar.test.js", "test/plugin/isTomorrow.test.js", "test/locale/hu.test.js", "test/timezone.test.js:UTC and utcOffset", "test/plugin/arraySupport.test.js", "test/locale/zh.test.js", "test/plugin/isToday.test.js", "test/plugin/declarations.test.js", "test/locale/hr.test.js", "test/plugin/timezone.test.js", "test/plugin/badMutable.test.js", "test/locale.test.js", "test/plugin/customParseFormat.test.js", "test/locale/ru.test.js", "test/plugin/duration.test.js", "test/plugin/isoWeek.test.js", "test/plugin/minMax.test.js", "test/plugin/dayOfYear.test.js", "test/plugin/isoWeeksInYear.test.js", "test/timezone.test.js:UTC add day in DST", "test/plugin/buddhistEra.test.js", "test/locale/uk.test.js", "test/locale/cs.test.js", "test/display.test.js", "test/manipulate.test.js", "test/locale/lt.test.js", "test/locale/zh-cn.test.js", "test/locale/en.test.js", "test/plugin/isBetween.test.js"], "failed_tests": [], "skipped_tests": []}
{"passed_count": 69, "failed_count": 1, "skipped_count": 0, "passed_tests": ["test/timezone.test.js:Add Time days (DST)", "test/locale/de.test.js", "test/plugin.test.js", "test/get-set.test.js", "test/plugin/utc.test.js", "test/plugin/quarterOfYear.test.js", "test/plugin/objectSupport.test.js", "test/locale/fi.test.js", "test/locale/sk.test.js", "test/locale/sv.test.js", "test/plugin/advancedFormat.test.js", "test/plugin/toArray.test.js", "test/plugin/weekYear.test.js", "test/timezone.test.js", "test/plugin/isSameOrBefore.test.js", "test/timezone.test.js:Utc Offset", "test/plugin/pluralGetSet.test.js", "test/timezone.test.js:Diff (DST)", "test/locale/keys.test.js", "test/locale/sr-cyrl.test.js", "test/locale/br.test.js", "test/utils.test.js", "test/plugin/utc-utcOffset.test.js", "test/parse.test.js", "test/plugin/relativeTime.test.js", "test/plugin/isMoment.test.js", "test/plugin/isYesterday.test.js", "test/locale/pl.test.js", "test/plugin/toObject.test.js", "test/locale/sr.test.js", "test/plugin/localizedFormat.test.js", "test/plugin/updateLocale.test.js", "test/constructor.test.js", "test/plugin/weekday.test.js", "test/plugin/isSameOrAfter.test.js", "test/plugin/weekOfYear.test.js", "test/comparison.test.js", "test/plugin/isLeapYear.test.js", "test/query.test.js", "test/plugin/localeData.test.js", "test/locale/et.test.js", "test/locale/hu.test.js", "test/plugin/calendar.test.js", "test/plugin/isTomorrow.test.js", "test/timezone.test.js:UTC and utcOffset", "test/plugin/arraySupport.test.js", "test/locale/zh.test.js", "test/plugin/isToday.test.js", "test/plugin/declarations.test.js", "test/locale/hr.test.js", "test/plugin/badMutable.test.js", "test/locale.test.js", "test/plugin/customParseFormat.test.js", "test/locale/ru.test.js", "test/plugin/duration.test.js", "test/plugin/isoWeek.test.js", "test/plugin/minMax.test.js", "test/plugin/dayOfYear.test.js", "test/plugin/isoWeeksInYear.test.js", "test/timezone.test.js:UTC add day in DST", "test/locale/uk.test.js", "test/manipulate.test.js", "test/locale/cs.test.js", "test/plugin/buddhistEra.test.js", "test/display.test.js", "test/locale/lt.test.js", "test/locale/zh-cn.test.js", "test/locale/en.test.js", "test/plugin/isBetween.test.js"], "failed_tests": ["test/plugin/timezone.test.js"], "skipped_tests": []}
{"passed_count": 70, "failed_count": 0, "skipped_count": 0, "passed_tests": ["test/timezone.test.js:Add Time days (DST)", "test/plugin.test.js", "test/get-set.test.js", "test/locale/de.test.js", "test/plugin/utc.test.js", "test/plugin/quarterOfYear.test.js", "test/plugin/objectSupport.test.js", "test/locale/fi.test.js", "test/locale/sk.test.js", "test/locale/sv.test.js", "test/plugin/advancedFormat.test.js", "test/plugin/weekYear.test.js", "test/plugin/toArray.test.js", "test/timezone.test.js", "test/plugin/isSameOrBefore.test.js", "test/timezone.test.js:Utc Offset", "test/plugin/pluralGetSet.test.js", "test/timezone.test.js:Diff (DST)", "test/plugin/utc-utcOffset.test.js", "test/locale/sr-cyrl.test.js", "test/utils.test.js", "test/locale/br.test.js", "test/plugin/relativeTime.test.js", "test/parse.test.js", "test/locale/keys.test.js", "test/plugin/isMoment.test.js", "test/plugin/isYesterday.test.js", "test/locale/pl.test.js", "test/plugin/toObject.test.js", "test/locale/sr.test.js", "test/plugin/localizedFormat.test.js", "test/plugin/updateLocale.test.js", "test/constructor.test.js", "test/plugin/weekday.test.js", "test/plugin/isSameOrAfter.test.js", "test/plugin/weekOfYear.test.js", "test/comparison.test.js", "test/plugin/isLeapYear.test.js", "test/query.test.js", "test/plugin/localeData.test.js", "test/plugin/calendar.test.js", "test/plugin/isTomorrow.test.js", "test/locale/et.test.js", "test/locale/hu.test.js", "test/timezone.test.js:UTC and utcOffset", "test/plugin/arraySupport.test.js", "test/locale/zh.test.js", "test/plugin/isToday.test.js", "test/plugin/declarations.test.js", "test/locale/hr.test.js", "test/plugin/timezone.test.js", "test/locale.test.js", "test/plugin/badMutable.test.js", "test/plugin/customParseFormat.test.js", "test/locale/ru.test.js", "test/plugin/isoWeek.test.js", "test/plugin/duration.test.js", "test/plugin/minMax.test.js", "test/plugin/dayOfYear.test.js", "test/plugin/isoWeeksInYear.test.js", "test/timezone.test.js:UTC add day in DST", "test/manipulate.test.js", "test/display.test.js", "test/locale/uk.test.js", "test/plugin/buddhistEra.test.js", "test/locale/cs.test.js", "test/locale/lt.test.js", "test/locale/zh-cn.test.js", "test/locale/en.test.js", "test/plugin/isBetween.test.js"], "failed_tests": [], "skipped_tests": []}