vim-patch:8.0.0735: no indication that the quickfix window/buffer changed

Problem:    There is no way to notice that the quickfix window contents has
            changed.
Solution:   Increment b:changedtick when updating the quickfix window.
            (Yegappan Lakshmanan)
a8788f4d0b

src/nvim/quickfix.c

@@ -2887,6 +2887,7 @@ static void qf_update_buffer(qf_info_T *qi, qfline_T *old_last)
     qf_update_win_titlevar(qi);
 
     qf_fill_buffer(qi, buf, old_last);
+    buf_inc_changedtick(buf);
 
     if (old_last == NULL) {
       (void)qf_win_pos_update(qi, 0);