fix: Update Swedish locale (sv) fix ordinal error
fix #743
**Describe the bug**
When using the format for ordinal numbers (`Do`) in Swedish the formatting is wrong for 1 and 2. It becomes `am` instead of `a`. This is likely because the date is formatted a second time, and `a` is formatted to be `am`. 

What happens:
`> dayjs('2019-01-01').locale('sv').format('dddd Do MMMM')`
'tisdag 1am januari'

`> dayjs('2019-01-02').locale('sv').format('dddd Do MMMM')`
'onsdag 2am januari'

`> dayjs('2019-01-03').locale('sv').format('dddd Do MMMM')`
'torsdag 3e januari'

**Expected behavior**
I expect `1st` to be `1a` and `2nd` to be `2a`
`> dayjs('2019-01-01').locale('sv').format('dddd Do MMMM')`
'tisdag 1a januari'

`> dayjs('2019-01-02').locale('sv').format('dddd Do MMMM')`
'onsdag 2a januari'

`> dayjs('2019-01-03').locale('sv').format('dddd Do MMMM')`
'torsdag 3e januari'

**Information**
 - Day.js Version 1.8.17
 - OS: MacOS Mojave 10.14.5
 - Browser: Chrome 78
 - Time zone: GMT+1

Ordinal formatting in Swedish
diff --git a/src/locale/sv.js b/src/locale/sv.js
index 288c953d3..cd2d46451 100644
--- a/src/locale/sv.js
+++ b/src/locale/sv.js
@@ -11,7 +11,7 @@ const locale = {
   ordinal: (n) => {
     const b = n % 10
     const o = (b === 1) || (b === 2) ? 'a' : 'e'
-    return `${n}${o}`
+    return `[${n}${o}]`
   },
   formats: {
     LT: 'HH:mm',

diff --git a/test/locale/sv.test.js b/test/locale/sv.test.js
new file mode 100644
index 000000000..31c15660f
--- /dev/null
+++ b/test/locale/sv.test.js
@@ -0,0 +1,21 @@
+import MockDate from 'mockdate'
+import dayjs from '../../src'
+import advancedFormat from '../../src/plugin/advancedFormat'
+import '../../src/locale/sv'
+
+dayjs.extend(advancedFormat)
+
+beforeEach(() => {
+  MockDate.set(new Date())
+})
+
+afterEach(() => {
+  MockDate.reset()
+})
+
+it('Swedish locale Do 1a not format to 1am', () => {
+  expect(dayjs('2019-01-01').locale('sv').format('dddd Do MMMM'))
+    .toBe('tisdag 1a januari')
+  expect(dayjs('2019-01-02').locale('sv').format('dddd Do MMMM'))
+    .toBe('onsdag 2a januari')
+})

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