[Backend Dependencies Update] Update flask-socketio to 4.2.1

[pyup-bot]

This PR updates flask-socketio from 4.0.0 to 4.2.1.

Changelog

4.2.1

- Add support for Apache Kafka message queue [700](https://github.com/miguelgrinberg/flask-socketio/issues/700) ([commit](https://github.com/miguelgrinberg/flask-socketio/commit/f20268a3ec14af3e8d6681c2ffd01e299dc4f6df)) (thanks **Vincent Mézino**!)
- Update CORS documentation ([commit](https://github.com/miguelgrinberg/flask-socketio/commit/d9cd34a86dedf96ca5232cf981b54b4c1c6e362d))

4.2.0

- Address potential websocket cross-origin attacks [128](https://github.com/miguelgrinberg/python-engineio/issues/128) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/7548f704a0a3000b7ac8a6c88796c4ae58aa9c37))
- Documentation for the Same Origin security policy ([commit](https://github.com/miguelgrinberg/flask-socketio/commit/42d4e02055f5936f1322982bf44a845987d75144))

4.1.1

- Fix typo in "Using nginx" section [1007](https://github.com/miguelgrinberg/flask-socketio/issues/1007) ([commit](https://github.com/miguelgrinberg/flask-socketio/commit/9e152b24ec30dd712886c4da3ec6a3aded855a00)) (thanks **Steffen Schneider**!)
- updated python-socketio min version requirement to 4.0.0 [1006](https://github.com/miguelgrinberg/flask-socketio/issues/1006) ([commit](https://github.com/miguelgrinberg/flask-socketio/commit/40a34c119a6b7f7e00d2a476d26e985cbd10ec19)) (thanks **Shantanu Hazari**!)

4.1.0

- Add ConnectionRefusedError exception from python-socketio [989](https://github.com/miguelgrinberg/flask-socketio/issues/989) ([commit](https://github.com/miguelgrinberg/flask-socketio/commit/3f9fda8f0de551567834400ff72a95c10c7d42b4))
- Invoke Socket.IO callbacks with app and request context [262](https://github.com/miguelgrinberg/flask-socketio/issues/262) ([commit](https://github.com/miguelgrinberg/flask-socketio/commit/75a75d47cb20fca8a8b2b2818a7602d43b4cea1f))
- Copy handler's name and docstring to handler wrapper [573](https://github.com/miguelgrinberg/flask-socketio/issues/573) ([commit](https://github.com/miguelgrinberg/flask-socketio/commit/4e0329b59e653edc19b31f05823b47bd63c0bc72))
- Less aggressive monkey patching for gevent [413](https://github.com/miguelgrinberg/flask-socketio/issues/413) ([commit](https://github.com/miguelgrinberg/flask-socketio/commit/55d02d97708bd91b7d8f761ab57aba8d946039ff))
- Updates jquery and socket.io in example application [988](https://github.com/miguelgrinberg/flask-socketio/issues/988) ([commit](https://github.com/miguelgrinberg/flask-socketio/commit/67da0d6627149c27da4ddc9b675aacf946dc3588)) (thanks **sillyfrog**!)

Links

• PyPI: https://pypi.org/project/flask-socketio
• Changelog: https://pyup.io/changelogs/flask-socketio/
• Repo: http://github.com/miguelgrinberg/Flask-SocketIO/
• Docs: https://pythonhosted.org/Flask-SocketIO/

[pyup-bot]

Closing this in favor of #831