Cache public/assets if rake assets:clean_expired is successful
Merge branch 'master' of git://github.com/heroku/heroku-buildpack-ruby into update
Merge pull request #1 from DouweM/update

Update to heroku-buildpack-ruby v50
Merge remote-tracking branch 'upstream/master'
Merge pull request #2 from swrobel/master

Merge latest from upstream (heroku/heroku-buildpack-ruby)
support for turbo-sprockets-rails3