rubocop: add rubocop-rails dependency
rubocop: add rubocop-rails dependency

Otherwise we can't find many cops. I'm not sure why this is necessary
with the newer versions of the gem but not the old.

Mokolea/git-scm.com,mosoft521/gitscm-next,git/git-scm.com,Mokolea/git-scm.com,Mokolea/git-scm.com,mosoft521/gitscm-next,mosoft521/gitscm-next,git/git-scm.com,git/git-scm.com,git/git-scm.com,mosoft521/gitscm-next,Mokolea/git-scm.com