Fix RedirectView.permanent

To drop Django warning.

costs/urls.py

@@ -5,7 +5,7 @@ from . import views
 
 urlpatterns = [
     url(r'^$',
-        RedirectView.as_view(pattern_name='list-documents'),
+        RedirectView.as_view(pattern_name='list-documents', permanent=False),
         name='index'),
     url(r'^documents/(?P<pk>\d+)',
         views.detail_document,