customParseFormat doesn't work when format doesn't fit the Date

[](https://issuehunt.io/r/iamkun/dayjs/issues/605)

`
dayjs('2019/04/19, 'MMDDYY').isValid()
`
returns true
and it parses to Wed Jul 20 2005.

Moment.js does not parse it.

https://jsfiddle.net/3meh8g0k/

You can get the same results using other different formats (e.g dayjs('2019/04/19, 'MM' returns Mon May 20 2019)

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### Submitted pull Requests
- [#866 Consider using Intl api and update customParseFormat](https://issuehunt.io/r/iamkun/dayjs/pull/866)
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