new Dayjs with string in Korean that cause invalid date

**Describe the bug**
korean using this format "YYYY.MM.DD."
when I run this , dayjs("2022.06.20.") , it returns invalid date.

Maybe this line's regex should support more format?
https://github.com/iamkun/dayjs/blob/74e82b9da5ec8b90361fc27ac7c8b63faf354502/src/index.js#L66

**Expected behavior**
new dayjs() returns a valid date.

**Information**
- Day.js Version any
- Browser Edge 18

Start with the date parsing logic in src/index.js at the linked line and reproduce the issue using dayjs("2022.06.20."). Check how the current regular expression handles the trailing period in the Korean date format. Done means this input returns a valid date without breaking existing parsing behavior.

Written by the indexing model from the issue text.