Refactor primary_key_field_name

Author: DannyAziz

django_elasticsearch_dsl/documents.py

@@ -69,7 +69,7 @@ def get_queryset(self):
         """
         Return the queryset that should be indexed by this doc type.
         """
-        primary_key_field_name = self.django.model_meta.pk.name
+        primary_key_field_name = self.django.model._meta.pk.name
         return self.django.model._default_manager.all().order_by(primary_key_field_name)
 
     def prepare(self, instance):