Enable lua checkers in syntastic

dotfiles/vim/vimrc

   \ "active_filetypes": ["bash"],
   \ "passive_filetypes": ["python"] }
 
+let g:syntastic_check_on_open = 1
+let g:syntastic_lua_checkers = ["luac", "luacheck"]
+let g:syntastic_lua_luacheck_args = "--no-unused-args"
+
 let g:gitgutter_sign_added = '✚'
 let g:gitgutter_sign_modified = '❱'
 let g:gitgutter_sign_removed = '❌'