fix: support parsing unlimited decimals of millisecond
fix #544


support parsing 
```
dayjs('2019-03-25T06:41:00.999999999')
```
**Describe the bug**
When I use the UTC-Plugin and try to parse a string with milliseconds, it changes the time (I'm CET). If I append a "Z" to my string, this does not happen (see example)

**Expected behavior**
Parsing a string without milliseconds creates a correct representation of the date (with or without "Z" at the end). Adding milliseconds to the script should not change this behavior.

**Example**
```
dayjs.utc('2019-03-25T06:41:00');
/** { [Number: 1553496060000]
      '$L': 'en',
      '$u': true,
      '$d': 2019-03-25T06:41:00.000Z,
      '$y': 2019,
      '$M': 2,
      '$D': 25,
      '$W': 1,
      '$H': 6,
      '$m': 41,
      '$s': 0,
      '$ms': 0 }
*/

dayjs.utc('2019-03-25T06:41:00Z');
/** { [Number: 1553496060000]
      '$L': 'en',
      '$u': true,
      '$d': 2019-03-25T06:41:00.000Z,
      '$y': 2019,
      '$M': 2,
      '$D': 25,
      '$W': 1,
      '$H': 6,
      '$m': 41,
      '$s': 0,
      '$ms': 0 }
*/
// They are the same

dayjs.utc('2019-03-25T06:41:00.654321');
// This one is one hour of (the first example isn't)
/** { [Number: 1553492460654]
      '$L': 'en',
      '$u': true,
      '$d': 2019-03-25T05:41:00.654Z,
      '$y': 2019,
      '$M': 2,
      '$D': 25,
      '$W': 1,
      '$H': 5,
      '$m': 41,
      '$s': 0,
      '$ms': 654 }
*/

dayjs.utc('2019-03-25T06:41:00.654321Z')
// This one isn't one hour off (as I would expect it for the previous one too)
/** { [Number: 1553496060654]
      '$L': 'en',
      '$u': true,
      '$d': 2019-03-25T06:41:00.654Z,
      '$y': 2019,
      '$M': 2,
      '$D': 25,
      '$W': 1,
      '$H': 6,
      '$m': 41,
      '$s': 0,
      '$ms': 654 }
*/
```

**Information**
 - Day.js Version: v1.8.11
 - OS: Windows 10
 - Browser: Chrome, Jest

UTC Plugin Milliseconds parsing
diff --git a/src/constant.js b/src/constant.js
index 6cab7bee5..a4f034fa2 100644
--- a/src/constant.js
+++ b/src/constant.js
@@ -26,5 +26,5 @@ export const FORMAT_DEFAULT = 'YYYY-MM-DDTHH:mm:ssZ'
 export const INVALID_DATE_STRING = 'Invalid Date'
 
 // regex
-export const REGEX_PARSE = /^(\d{4})[-/]?(\d{1,2})?[-/]?(\d{0,2})[^0-9]*(\d{1,2})?:?(\d{1,2})?:?(\d{1,2})?.?(\d{1,3})?$/
+export const REGEX_PARSE = /^(\d{4})[-/]?(\d{1,2})?[-/]?(\d{0,2})[^0-9]*(\d{1,2})?:?(\d{1,2})?:?(\d{1,2})?.?(\d+)?$/
 export const REGEX_FORMAT = /\[([^\]]+)]|Y{2,4}|M{1,4}|D{1,2}|d{1,4}|H{1,2}|h{1,2}|a|A|m{1,2}|s{1,2}|Z{1,2}|SSS/g
diff --git a/src/index.js b/src/index.js
index f8517ac38..af7aae3a4 100644
--- a/src/index.js
+++ b/src/index.js
@@ -60,12 +60,13 @@ const parseDate = (cfg) => {
     const d = date.match(C.REGEX_PARSE)
     if (d) {
       const m = d[2] - 1 || 0
+      const ms = (d[7] || '0').substring(0, 3)
       if (utc) {
         return new Date(Date.UTC(d[1], m, d[3]
-          || 1, d[4] || 0, d[5] || 0, d[6] || 0, d[7] || 0))
+          || 1, d[4] || 0, d[5] || 0, d[6] || 0, ms))
       }
       return new Date(d[1], m, d[3]
-          || 1, d[4] || 0, d[5] || 0, d[6] || 0, d[7] || 0)
+          || 1, d[4] || 0, d[5] || 0, d[6] || 0, ms)
     }
   }
 

diff --git a/test/parse.test.js b/test/parse.test.js
index 6302d8942..aecbaa898 100644
--- a/test/parse.test.js
+++ b/test/parse.test.js
@@ -81,6 +81,14 @@ describe('Parse', () => {
     expect(normalized.toISOString()).toEqual(expected)
   })
 
+  it('parses unlimited millisecond', () => {
+    const date = '2019-03-25T06:41:00.999999999'
+    const ds = dayjs(date)
+    const ms = moment(date)
+    expect(ds.valueOf()).toEqual(ms.valueOf())
+    expect(ds.millisecond()).toEqual(ms.millisecond())
+  })
+
   it('String Other, Null and isValid', () => {
     global.console.warn = jest.genMockFunction()// moment.js otherString will throw warn
     expect(dayjs('otherString').toString().toLowerCase()).toBe(moment('otherString').toString().toLowerCase())
@@ -134,4 +142,10 @@ describe('REGEX_PARSE', () => {
     expect(dayjs(date).valueOf()).toBe(moment(date).valueOf())
     expect(d.join('-')).toBe('2020/9/30-2020-9-30----')
   })
+  it('2019-03-25T06:41:00.999999999', () => {
+    const date = '2019-03-25T06:41:00.999999999'
+    const d = date.match(REGEX_PARSE)
+    expect(dayjs(date).valueOf()).toBe(moment(date).valueOf())
+    expect(d.join('-')).toBe('2019-03-25T06:41:00.999999999-2019-03-25-06-41-00-999999999')
+  })
 })
diff --git a/test/plugin/utc.test.js b/test/plugin/utc.test.js
index 4aaacd3ea..a02e8c143 100644
--- a/test/plugin/utc.test.js
+++ b/test/plugin/utc.test.js
@@ -94,6 +94,14 @@ describe('Parse UTC ', () => {
     expect(dayjs.utc(d).format()).toEqual('2018-09-06T19:34:28Z')
     expect(dayjs.utc(d).format()).toEqual(moment.utc(d).format())
   })
+
+  it('parses unlimited millisecond in utc', () => {
+    const date = '2019-03-25T06:41:00.999999999'
+    const ds = dayjs.utc(date)
+    const ms = moment.utc(date)
+    expect(ds.valueOf()).toEqual(ms.valueOf())
+    expect(ds.millisecond()).toEqual(ms.millisecond())
+  })
 })
 
 it('Clone retains the UTC mode', () => {

{"test/parse.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/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/sk.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/sv.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/advancedFormat.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/toArray.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/timezone.test.js:Utc Offset": {"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/plugin/utc-utcOffset.test.js": {"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/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/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/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/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/plugin/isTomorrow.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/calendar.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/et.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/zh.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isToday.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/declarations.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/badMutable.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/customParseFormat.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/ru.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/dayOfYear.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/timezone.test.js:UTC add day in DST": {"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/plugin/buddhistEra.test.js": {"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/zh-cn.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/en.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isBetween.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}}
{"test/parse.test.js": {"run": "PASS", "test": "FAIL", "fix": "PASS"}}
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