Made the test timezone aware, DateTimeFiled(auto_now_add) already was.

lostplaces/lostplaces_app/tests/models/test_voucher_model.py

@@ -2,6 +2,7 @@ import datetime
 
 from django.test import TestCase
 from django.db import models
+from django.utils import timezone
 
 from lostplaces_app.models import Voucher
 from lostplaces_app.tests.models import ModelTestCase
@@ -10,7 +11,7 @@ from lostplaces_app.tests.models import ModelTestCase
 def mock_voucher():
     return Voucher.objects.create(
         code='ayDraJCCwfhcFiYmSR5GrcjcchDfcahv',
-        expires_when=datetime.datetime.now() + datetime.timedelta(days=1)
+        expires_when=timezone.now() + datetime.timedelta(days=1)
     )