Fixed #26013 -- Moved django.core.urlresolvers to django.urls.

Thanks to Tim Graham for the review.

tests/generic_views/models.py

@@ -1,7 +1,7 @@
-from django.core.urlresolvers import reverse
 from django.db import models
 from django.db.models import QuerySet
 from django.db.models.manager import BaseManager
+from django.urls import reverse
 from django.utils.encoding import python_2_unicode_compatible