Now parsing file on insert mode leave as well

We used to do it on buffer enter and cursor hold. Doing it on insert leave too
produces much quicker compilation error feedback when editing C-family code
because the user doesn't have to wait for the next cursor hold event.

autoload/youcompleteme.vim

@@ -333,6 +333,7 @@ function! s:OnInsertLeave()
 
   let s:omnifunc_mode = 0
   call s:UpdateDiagnosticNotifications()
+  call s:OnFileReadyToParse()
   py ycm_state.OnInsertLeave()
   if g:ycm_autoclose_preview_window_after_completion ||
         \ g:ycm_autoclose_preview_window_after_insertion