chore(deps): bump tornado from 6.4 to 6.4.1 in /docs

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.4 to 6.4.1.
- [Changelog](https://github.com/tornadoweb/tornado/blob/master/docs/releases.rst)
- [Commits](tornadoweb/tornado@v6.4.0...v6.4.1)

---
updated-dependencies:
- dependency-name: tornado
  dependency-type: indirect
...

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

docs/requirements.txt

@@ -118,7 +118,7 @@ tabulate==0.9.0
     # via docstrfmt
 toml==0.10.2
     # via docstrfmt
-tornado==6.4
+tornado==6.4.1
     # via livereload
 typing-extensions==4.9.0
     # via