Fix tests views DjangoFilterBackend import

Author: pkolios

tests/django_restframework_gis_tests/views.py

@@ -1,5 +1,5 @@
+from django_filters.rest_framework import DjangoFilterBackend
 from rest_framework import generics
-from rest_framework.filters import DjangoFilterBackend
 from rest_framework_gis.filters import *
 from rest_framework_gis.pagination import GeoJsonPagination