subdomain type using ghday start date & end date is not the same as locale

[ChiaYuSu]

I don't know if it's because I didn't set locale: 'zh-tw' in date is not set to locale: 'zh-tw', so the problem is caused by
start date is not start at 2022/01/01, is start at 2022/01/02

But if I set loacle: 'zh-tw' console, the following problem occurs

[wa0x6e]

as explained in the docs, domain start and end is not guaranteed to be exactly the first and last day of the month

https://cal-heatmap.com/docs/options/subDomain#ghday

it's snapped to the last and first week of the month, to avoid duplicate columns on navigation

It's not a locale issue

[wa0x6e]

Docs has been updated to highlight this point

Issue #325 may fix this issue in some case