Fix lint error

Author: jkimbo

graphene_django/types.py

@@ -1,5 +1,7 @@
+import six
 from collections import OrderedDict
 
+from django.db.models import Model
 from django.utils.functional import SimpleLazyObject
 from graphene import Field
 from graphene.relay import Connection, Node
@@ -11,6 +13,10 @@
 from .utils import DJANGO_FILTER_INSTALLED, get_model_fields, is_valid_django_model
 
 
+if six.PY3:
+    from typing import Type
+
+
 def construct_fields(model, registry, only_fields, exclude_fields):
     _model_fields = get_model_fields(model)