Travis CI: run brew audit and brew audit --strict

Travis CI: run `brew audit` and `brew audit --strict` for all formulae in the current repo.

Errors from `brew audit --strict` are silenced.

Pull Request: #387

.travis.yml

@@ -99,6 +99,8 @@ matrix:
 
 script:
   - brew style linuxbrew/xorg
+  - brew audit $(cd $(brew --repo linuxbrew/xorg)/Formula; ls *.rb | sed 's|.rb$||')
+  - brew audit --strict $(cd $(brew --repo linuxbrew/xorg)/Formula; ls *.rb | sed 's|.rb$||') || true
 
 notifications:
   email: