Changing Vundle "Bundle" references to "Plugin"

Vundle is changing their interface from `Bundle*` to `Plugin*`.
See https://github.com/gmarik/Vundle.vim/blob/v0.10.2/doc/vundle.txt#L372-L396 for more information on this.
Merge pull request #95 from cassava/patch-1

Changing Vundle "Bundle" references to "Plugin"