Fix flake8 and isort errors

Note, isort now has default behaviour of searching recursively so we no
longer need the `-rc` flag

tests/app/models/test_base_model.py

@@ -64,6 +64,7 @@ def test_model_doesnt_swallow_attribute_errors(json_response):
 
     class Custom(JSONModel):
         ALLOWED_PROPERTIES = set()
+
         @property
         def foo(self):
             raise AttributeError('Something has gone wrong')