Bump tornado from 4.4.1 to 6.3.3 in /app

Bumps [tornado](https://github.com/tornadoweb/tornado) from 4.4.1 to 6.3.3.
- [Changelog](https://github.com/tornadoweb/tornado/blob/master/docs/releases.rst)
- [Commits](https://github.com/tornadoweb/tornado/compare/v4.4.1...v6.3.3)

---
updated-dependencies:
- dependency-name: tornado
  dependency-type: direct:production
...

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

app/requirements.txt

@@ -22,7 +22,7 @@ requests>=2.20.0
 singledispatch==3.4.0.3
 six==1.10.0
 socketIO-client==0.7.0
-tornado==4.4.1
+tornado==6.3.3
 websocket-client==0.37.0
 Werkzeug==2.2.3