Adds `vim-ruby` back to `vimrc.bundles`

Removal in https://github.com/thoughtbot/dotfiles/commit/deb7ee5948a0df56c2a68fc2dab22fd31d70a204
was accidental.

Also, removes `vim/bundle` directory as it is no longer useful to us, since
`vundle` creates it when it needs to.
Merge remote-tracking branch 'upstream/master'