fix flask context

hapic/ext/flask/context.py

         return FLASK_RE_PATH_URL.sub(r'{\1}', contextualised_rule)
 
     def by_pass_output_wrapping(self, response: typing.Any) -> bool:
+        from flask import Response
         return isinstance(response, Response)

tests/func/fake_api/test_flask.py

     )
 
     assert doc == SWAGGER_DOC_API
-    resp = app.get('/about')
+    resp = app.get('/about', status='*')
     assert resp.status_int == 200
     assert resp.json == {'datetime': '2017-12-07T10:55:08.488996+00:00',
                          'version': '1.2.3'}