fix: incorrect startOf/endOf behavior with +00:00 timezone

[sevtdy]

assume I'm in +08:00, when I parse time string with any regions in +00:00(like UTC, Africa/Abidjan), got the incorrect result

example:
incorrect in dayjs:

dayjs.tz('2021-04-01', 'Asia/Hong_Kong').endOf('day').format()
// "2021-04-01T23:59:59+08:00"
dayjs.tz('2021-04-01', 'Africa/Abidjan').endOf('day').format()
// "2021-04-01T15:59:59Z"
dayjs.tz('2021-04-01', 'UTC').endOf('day').format()
// "2021-04-01T15:59:59Z"

expect work like moment

moment.tz('2021-04-01', 'Asia/Hong_Kong').endOf('day').format()
// "2021-04-01T23:59:59+08:00"
moment.tz('2021-04-01', 'Africa/Abidjan').endOf('day').format()
// "2021-04-01T23:59:59Z"
moment.tz('2021-04-01', 'UTC').endOf('day').format()
// "2021-04-01T23:59:59Z"

[iamkun]

i'll reopen this pr to trigger a CI test

[iamkun]

Can you close this and re-open a new PR, please?

There might be some problem with Github CI trigger

[sevtdy]

sure.