Fixed six import

Author: syrusakbary

graphene/test/__init__.py

@@ -1,8 +1,9 @@
-from graphene.types.schema import Schema
-
+import six
 from graphql.error import format_error as format_graphql_error
 from graphql.error import GraphQLError
 
+from graphene.types.schema import Schema
+
 
 def default_format_error(error):
     if isinstance(error, GraphQLError):