Don't force translating attribute names.

This attribute key translation was advertised to be "off by default",
but was in fact forced in parser. This commit makes it obey
JSON_API_FORMAT_KEYS setting.

Author: amw

rest_framework_json_api/parsers.py

@@ -29,11 +29,11 @@ class JSONParser(parsers.JSONParser):
 
     @staticmethod
     def parse_attributes(data):
-        return utils.format_keys(data.get('attributes'), 'underscore') if data.get('attributes') else dict()
+        return utils.format_keys(data.get('attributes')) if data.get('attributes') else dict()
 
     @staticmethod
     def parse_relationships(data):
-        relationships = (utils.format_keys(data.get('relationships'), 'underscore')
+        relationships = (utils.format_keys(data.get('relationships'))
                          if data.get('relationships') else dict())
 
         # Parse the relationships