dj2: fix include in urls.py (#36895)

remove RemovedInDjango20Warning:
Passing a 3-tuple to django.conf.urls.include() is deprecated.
Pass a 2-tuple containing the list of patterns and app_name, and provide the
namespace argument to include() instead.

combo/urls.py

@@ -31,7 +31,7 @@ from . import plugins
 urlpatterns = [
     url(r'^manage/', decorated_includes(manager_required,
         include(combo_manager_urls))),
-    url(r'^admin/', include(admin.site.urls)),
+    url(r'^admin/', admin.site.urls),
     url(r'^logout/$', logout, name='auth_logout'),
     url(r'^login/$', login, name='auth_login'),
     url(r'^404$', error404),