Use cache.directories instead of `cache: bundler`
Use cache.directories instead of `cache: bundler`

We are overriding `install`, so gems weren't cached correctly.

GistIcon/travis-core,GistIcon/travis-core,Tiger66639/travis-core,GistIcon/travis-core,developerfm/travis-core,travis-ci/travis-core,travis-ci/travis-core,developerfm/travis-core,Tiger66639/travis-core,Tiger66639/travis-core,travis-ci/travis-core,developerfm/travis-core