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

Thanks to Tim Graham for the review.

tests/admin_views/test_adminsite.py

@@ -5,9 +5,9 @@ import datetime
 from django.conf.urls import url
 from django.contrib import admin
 from django.contrib.auth.models import User
-from django.core.urlresolvers import reverse
 from django.test import TestCase, override_settings
 from django.test.client import RequestFactory
+from django.urls import reverse
 
 from .models import Article