Merge fields used in meta attribute passed on DjangoObjectType

Author: Sebastian Hernandez

graphene_django/types.py

@@ -261,7 +261,10 @@ def __init_subclass_with_meta__(
         _meta.registry = registry
         _meta.filter_fields = filter_fields
         _meta.filterset_class = filterset_class
-        _meta.fields = django_fields
+        if _meta.fields:
+            _meta.fields.update(django_fields)
+        else:
+            _meta.fields = fields
         _meta.connection = connection
 
         super(DjangoObjectType, cls).__init_subclass_with_meta__(