Update auto_save.py

Fix for:
Exception in thread Thread-95:
Traceback (most recent call last):
  File ".\threading.py", line 532, in __bootstrap_inner
  File ".\threading.py", line 736, in run
  File ".\auto_save.py", line 37, in debounce_save
    if len(AutoSaveListener.save_queue) > 1:
RuntimeError: Must call on main thread, consider using sublime.set_timeout(function, timeout)