fix tests for python 3.6

tests/unit/test_decorator.py

         assert 'original_response' in response
         assert response['original_response'] == json.dumps({
             'message': 'We are testing',
-            'code': None,
             'details': {},
+            'code': None,
         })
 
     def test_unit__exception_handled__ok__exception_error_dict(self):
         assert 'original_response' in response
         assert response['original_response'] == json.dumps({
             'message': 'We are testing',
-            'code': None,
             'details': {'foo': 'bar'},
+            'code': None,
         })
 
     def test_unit__exception_handler__error__error_content_malformed(self):