core(minor): fix timezone warning when cleaning nonces

passbook/core/tasks.py

@@ -1,5 +1,5 @@
 """passbook core tasks"""
-from datetime import datetime
+from django.utils.timezone import now
 
 from structlog import get_logger
 
@@ -11,5 +11,5 @@ LOGGER = get_logger()
 @CELERY_APP.task()
 def clean_nonces():
     """Remove expired nonces"""
-    amount, _ = Nonce.objects.filter(expires__lt=datetime.now(), expiring=True).delete()
+    amount, _ = Nonce.objects.filter(expires__lt=now(), expiring=True).delete()
     LOGGER.debug("Deleted expired nonces", amount=amount)