Bump tornado from 6.1 to 6.4.2

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.1 to 6.4.2.
- [Changelog](https://github.com/tornadoweb/tornado/blob/v6.4.2/docs/releases.rst)
- [Commits](https://github.com/tornadoweb/tornado/compare/v6.1.0...v6.4.2)

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

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

requirements.txt

@@ -28,7 +28,7 @@ requests-oauthlib==1.3.0
 six==1.16.0
 slack-webhook==1.0.6
 toml==0.10.2
-tornado==6.1
+tornado==6.4.2
 tweepy==3.10.0
 tzlocal==2.1
 urllib3==1.26.5