Hook instead of monkeypatching bottles.

Make use of the new Homebrew bottle hooks 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.
Merge pull request #39 from mikemcquaid/homebrew-monkeypatching-cleanup

Cleanup monkeypatching bottles.