Bump tornado from 5.1.1 to 6.4.1

Bumps [tornado](https://github.com/tornadoweb/tornado) from 5.1.1 to 6.4.1.
- [Changelog](https://github.com/tornadoweb/tornado/blob/master/docs/releases.rst)
- [Commits](tornadoweb/tornado@v5.1.1...v6.4.1)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Diff for: requirements.txt

@@ -38,7 +38,7 @@ seaborn==0.9.0
 setuptools==65.5.1
 six==1.11.0
 statsmodels==0.9.0
-tornado==6.3.3
+tornado==6.4.1
 traitlets==4.3.2
 wcwidth==0.1.7
 wheel==0.38.1