redraw before s:warn

Author: blueyed

plug.vim

@@ -222,6 +222,7 @@ function! plug#end()
     let s:need_filetypeplugin_au = 1
   endif
   if !empty(warn)
+    redraw
     call s:warn('echom', printf('[vim-plug] "filetype %s on" should not be used manually with vim-plug, please remove it from your vimrc.', join(warn)))
   endif