extract_relationships may be static

Author: jsenecal

rest_framework_json_api/renderers.py

@@ -62,7 +62,8 @@ def extract_attributes(fields, resource):
 
         return utils.format_keys(data)
 
-    def extract_relationships(self, fields, resource, resource_instance):
+    @staticmethod
+    def extract_relationships(fields, resource, resource_instance):
         # Avoid circular deps
         from rest_framework_json_api.relations import ResourceRelatedField