Install default gems as travis_build_environment.user
Install default gems as travis_build_environment.user

travis_build_environment.user should own `$GEM_HOME`
Fixes https://github.com/travis-ci/travis-ci/issues/3662

vinaykaradia/travis-cookbook-cloned,Acidburn0zzz/travis-cookbooks,ardock/travis-cookbooks,ljharb/travis-cookbooks,Distelli/travis-cookbooks,travis-ci/travis-cookbooks,travis-ci/travis-cookbooks,dracos/travis-cookbooks,vinaykaradia/travis-cookbook-cloned,gavioto/travis-cookbooks,vinaykaradia/travis-cookbook-cloned,vinaykaradia/travis-cookbook-cloned,spurti-chopra/travis-cookbooks,Distelli/travis-cookbooks,ljharb/travis-cookbooks,ardock/travis-cookbooks,Zarthus/travis-cookbooks,ljharb/travis-cookbooks,gavioto/travis-cookbooks,Acidburn0zzz/travis-cookbooks,Distelli/travis-cookbooks,dracos/travis-cookbooks,Acidburn0zzz/travis-cookbooks,Zarthus/travis-cookbooks,vinaykaradia/travis-cookbook-cloned,Distelli/travis-cookbooks,Acidburn0zzz/travis-cookbooks,spurti-chopra/travis-cookbooks,gavioto/travis-cookbooks,spurti-chopra/travis-cookbooks,travis-ci/travis-cookbooks,Zarthus/travis-cookbooks,Zarthus/travis-cookbooks,gavioto/travis-cookbooks,ardock/travis-cookbooks,dracos/travis-cookbooks,dracos/travis-cookbooks,ardock/travis-cookbooks