Reexport utils.timezone imports

These are reexported by django.

django-stubs/utils/timezone.pyi

@@ -1,7 +1,7 @@
 # Stubs for django.utils.timezone (Python 3.5)
 
 from typing import Any, Optional, Union
-from datetime import tzinfo, datetime, timedelta
+from datetime import tzinfo as tzinfo, datetime as datetime, timedelta as timedelta
 from contextlib import ContextDecorator
 
 class UTC(tzinfo):