Fix platform detection for macOS

Author: rlue

plugin/barbaric.vim

@@ -1,5 +1,5 @@
 " Check dependencies
-if system('uname -s') == 'Darwin' && executable('xkbswitch')
+if has('mac') && executable('xkbswitch')
   let g:barbaric_ime = 'macos'
 elseif executable('fcitx-remote') && system('fcitx-remote') > 0
   let g:barbaric_ime = 'fcitx'