gems.rb syntax highlighting not working

When loading `gems.rb` files, I don't get any syntax highlighting, whereas I do with `gems.locked` (the filetype is `gemfilelock`).

I'm on Vim 7.4, using the latest HEAD of `vim-bundler` and [this](https://github.com/asymmetric/dotfiles/blob/master/vimrc) is my `.vimrc`.
