Bump tornado from 6.3.3 to 6.4.1

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.3.3 to 6.4.1.
- [Changelog](https://github.com/tornadoweb/tornado/blob/master/docs/releases.rst)
- [Commits](https://github.com/tornadoweb/tornado/compare/v6.3.3...v6.4.1)

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

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

requirements.txt

@@ -14,6 +14,6 @@ humanfriendly==9.1
 idna==2.10
 pytz==2021.1
 six==1.16.0
-tornado==6.3.3
+tornado==6.4.1
 tzlocal==2.1
 urllib3==1.26.18