Simplify neovim check

plug.vim

@@ -73,7 +73,7 @@ let s:plug_tab = get(s:, 'plug_tab', -1)
 let s:plug_buf = get(s:, 'plug_buf', -1)
 let s:mac_gui = has('gui_macvim') && has('gui_running')
 let s:is_win = has('win32') || has('win64')
-let s:nvim = exists('##JobActivity') && !s:is_win
+let s:nvim = has('nvim') && !s:is_win
 let s:me = resolve(expand('<sfile>:p'))
 let s:base_spec = { 'branch': 'master', 'frozen': 0 }
 let s:TYPE = {