add zh locale

[ZYinMD]

In window.navigator.languages in Chrome, there are 4 valid Chinese locales that could appear: zh, zh-cn, zh-cn, zh-hk. Currently zh is missing from dayjs. This PR adds the zh locale.

zh has some minor improvements over the other 3 locales. For developers, this won't affect your existing code, but if you start using zh, your output will be slightly more correct in some occasional cases.

For example:

// no more unecessary whitespace:
dayjs().locale('zh-cn').subtract(7, 'month').fromNow() // 7 个月前
dayjs().locale('zh').subtract(7, 'month').fromNow() // 7个月前

// use "后" instead of "内" for relative future:
dayjs().locale('zh-cn').add(3, 'day').fromNow() // 3 天内
dayjs().locale('zh').add(3, 'day').fromNow() // 3天后

// improve ordinal week of year:
dayjs('2020-10-13').locale('zh-tw').format('wo') // 42日 // wrong
dayjs('2020-10-13').locale('zh-hk').format('wo') // 42日 // wrong
dayjs('2020-10-13').locale('zh-cn').format('wo') // 42周 // ok
dayjs('2020-10-13').locale('zh').format('wo') // 第42周 // better

issue #820

[codecov]

Codecov Report

Merging #822 into dev will not change coverage.
The diff coverage is 100%.

@@         Coverage Diff         @@
##            dev   #822   +/-   ##
===================================
  Coverage   100%   100%           
===================================
  Files       157    158    +1     
  Lines      1148   1165   +17     
  Branches    215    222    +7     
===================================
+ Hits       1148   1165   +17

Impacted Files	Coverage Δ
src/locale/zh.js	100% <100%> (ø)

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[iamkun]

please add test

[ZYinMD]

Honestly I looked everywhere in the codebase and didn't find how it should be tested, and why existing tests are not passing... I compared with #516, which didn't add any tests either, and seems it did exactly the same thing as this one.

哭了

[iamkun]

test/locale/zh-cn.test.js

[iamkun]

Cool, I'll keep the same at this moment. And update it all together later.

[iamkun]

🎉 This PR is included in version 1.8.23 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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