Cleanup monkeypatching bottles.

Make use of the new Homebrew bottle monkeypatching module added in
https://github.com/Homebrew/homebrew/pull/27890 to make the
Boxen bottle handling more robust. Long-term we/you should really move
to using proper Homebrew bottles (with checksums and SSL) but this
should at least stop things getting broken periodically.

I'm aware this may be somewhat controversial so I'm open to other
approaches.