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.
Update for Vundle's new interface

See https://github.com/gmarik/Vundle.vim/blob/master/doc/vundle.txt#L345-L369
Ensure existing Vundle checkout is suitably up-to-date