Flake8 fixes

Author: adamcharnock

graphene/contrib/django/filter/__init__.py

@@ -1,5 +1,5 @@
 try:
-    import django_filters
+    import django_filters  # noqa
 except:
     raise Exception(
         "Use of django filtering requires the django-filter package "

graphene/contrib/django/types.py

@@ -29,9 +29,12 @@ def construct_fields(cls):
                 # We skip this field if we specify only_fields and is not
                 # in there. Or when we exclude this field in exclude_fields
                 continue
-            converted_field = convert_django_field(field)
+            converted_field = cls.convert_django_field(field)
             cls.add_to_class(field.name, converted_field)
 
+    def convert_django_field(cls, field):
+        return convert_django_field(field)
+
     def construct(cls, *args, **kwargs):
         cls = super(DjangoObjectTypeMeta, cls).construct(*args, **kwargs)
         if not cls._meta.abstract: