Bump werkzeug from 0.11.11 to 0.15.3 in /app

Bumps [werkzeug](https://github.com/pallets/werkzeug) from 0.11.11 to 0.15.3.
- [Release notes](https://github.com/pallets/werkzeug/releases)
- [Changelog](https://github.com/pallets/werkzeug/blob/master/CHANGES.rst)
- [Commits](https://github.com/pallets/werkzeug/compare/0.11.11...0.15.3)

Signed-off-by: dependabot[bot] <support@github.com>

app/requirements.txt

@@ -24,5 +24,5 @@ six==1.10.0
 socketIO-client==0.7.0
 tornado==4.4.1
 websocket-client==0.37.0
-Werkzeug==0.11.11
+Werkzeug==0.15.3