Add missing ":for => :osx" in OS X deps
Add missing comment from spotify.rb
Add deps to install vim on Ubuntu
Make Prezto deps platform-agnostic

Because Prezto just needs to be cloned to a directory, it doesn't
really add any value having the separate deps per platform.
Add deps to install Vundle

These deps, like Prezto, are also platform-agnostic, because the
installation only requires the cloning of a repository.