tap command: add -f alias to --force flag

[rrotter]

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Make brew tap -f == brew tap --force.

• Current behavior is to reject -f with Error: ambiguous option: -f, however the only conflict is the disabled --full flag.
• Improve consistency: tap is the only command with a --force option that isn't explicitly aliased w/ -f (see: git grep 'switch.*"--force"' Library/Homebrew)

[ZhongRuoyu]

Makes sense to me, thanks @rrotter!