Remove ag.vim since it's deprecated

See rking/ag.vim#124 (comment)

The auther recommended using the original ack.vim that is what ag.vim
was forked from.  I also remapped :ag to :Ack and set :Ack to use the ag
command if it's available.

vim/plugs.vim

@@ -19,16 +19,15 @@ Plug 'bling/vim-airline'
 Plug 'tpope/vim-sensible'
 
 " searching / grep - only loaded when invoked
-Plug 'mileszs/ack.vim', { 'on': 'Ack' }
-Plug 'rking/ag.vim', { 'on': 'Ag' }
+Plug 'mileszs/ack.vim', { 'on': ['Ack', 'Ag'] }
 
 " navigation
 Plug 'ctrlpvim/ctrlp.vim' " , { 'on': ['CtrlP', 'CtrlPBuffer', 'CtrlPMixed'] }
 " netrw has some bugs when using it as a "sidebar", so just use NerdTree for
 " now if I need it. Load on demand.
 Plug 'Xuyuanp/nerdtree-git-plugin', { 'on': 'NERDTreeToggle' }
 Plug 'scrooloose/nerdtree', { 'on': 'NERDTreeToggle' }
-Plug 'majutsushi/tagbar'
+Plug 'majutsushi/tagbar', { 'on': 'TagbarToggle' }
 
 " Syntax hilighting for various things
 Plug 'ekalinin/Dockerfile.vim' " , { 'for': 'dockerfile' }

vimrc

@@ -306,9 +306,15 @@ set title " Change the title in the terminal
 cmap w!! w !sudo tee % >/dev/null
 
 let g:ctrlp_cache_dir = $HOME . '/.cache/ctrlp' " Persist ctrlp cache to disk
-" If ag is installed, use it for ctrlp instead of the built in search
+
+" Check if ag (the_silver_searcher) is installed
 if executable('ag')
+ " If ag is installed, use it for ctrlp instead of the built in search
  let g:ctrlp_user_command = 'ag %s -l --nocolor -g ""'
+ " Also use it for ack.vim due to https:/rking/ag.vim/issues/124#issuecomment-227038003
+ let g:ackprg = 'ag --vimgrep --smart-case'
+ cnoreabbrev ag Ack
+ cnoreabbrev Ag Ack
 endif
 
 " For chef berkshelf