Fix `Pkg#uninstall` not calling `MacOS.undeletable?` for all files.

formula: Remove reference to homebrew/x11

Fix parsing extension from URL.

That tap is now defunct.

Signed-off-by: Bob W. Hogg <rwhogg@linux.com>

Delete `:focus`.

travis.yml: only build the master branch.

audit: Port patches audit code to a rubocop and add tests

This avoid two weird things:

- scary messages when building tags fails
- two builds being run instead of one when people create a PR and a
  branch on the Homebrew/brew repo (rather than their fork).

Detect `Tap` in `CaskLoader`.

audit: add additional php header ignore patterns

Tap.each: return an enumerable when no block given

Remove `brew cask _checkurl`.