Resolved RemovedInDjango20Warning deprecation warnings

netbox/tenancy/models.py

@@ -1,6 +1,6 @@
 from django.contrib.contenttypes.fields import GenericRelation
-from django.core.urlresolvers import reverse
 from django.db import models
+from django.urls import reverse
 from django.utils.encoding import python_2_unicode_compatible
 
 from extras.models import CustomFieldModel, CustomFieldValue