[vim] Add outdated plugin notification

nvim/init.vim

@@ -10,6 +10,10 @@ if empty(glob(data_dir . '/autoload/plug.vim'))
   autocmd VimEnter * PlugInstall --sync | source $MYVIMRC
 endif
 call plug#begin()
+
+" Warn about plugin updates
+Plug 'semanser/vim-outdated-plugins'
+
 " Powerline replacement
 Plug 'vim-airline/vim-airline'
 Plug 'vim-airline/vim-airline-themes'