Difference between locale DE monthsShort abbreviation and moment.js abbreviation

**Describe the bug**
DE locale abbreviations for monthsShort differ from Moment.js ones since a dot is missing at the end of months with more than 4 letters.
Same issue as with FR locale: https://github.com/iamkun/dayjs/issues/861

Here is the code line concerned:
https://github.com/iamkun/dayjs/blob/dev/src/locale/de.js#L32
```
monthsShort: 'Jan_Feb_März_Apr_Mai_Juni_Juli_Aug_Sept_Okt_Nov_Dez'.split('_'),
```

Here is the moment code for DE:
https://github.com/moment/moment/blob/develop/locale/de.js#L35
```
monthsShort: 'Jan._Feb._März_Apr._Mai_Juni_Juli_Aug._Sep._Okt._Nov._Dez.'.split(
'_'
),
```

**Expected behavior**
I expect to have the same abbreviations than Moment.js

**Information**
- Day.js Version: 1.8.15
- OS: 11.2.3
- Browser: chrome 95
- Time zone: GMT+01:00

Start in src/locale/de.js at the monthsShort definition on line 32, and compare it with the Moment.js German locale referenced in the issue. Done means the German short month names use the expected abbreviations, including periods where specified, while preserving the locale's month order.

Written by the indexing model from the issue text.