fix: startOf get error when use mutable & timezone & UTC

[snowtreetree]

when using plugins of mutable 、timezone、UTC， methods startOf get an error result.

dayjs.extend(utc)
dayjs.extend(timezone)
dayjs.extend(customParseFormat)

dayjs.extend(badMutable)

dayjs.tz('2009-12-31 23:59:59.999', 'America/New_York').endOf('day').format('YYYY-MM-DD HH:mm:ss.SSS')
// without badMutable 2009-12-31 23:59:59.999
// with badMutable 2010-01-02 01:59:59.999