Bump tornado from 6.4.1 to 6.4.2

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.4.1 to 6.4.2.
- [Changelog](https://github.com/tornadoweb/tornado/blob/v6.4.2/docs/releases.rst)
- [Commits](tornadoweb/tornado@v6.4.1...v6.4.2)

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

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

requirements.txt

@@ -67,7 +67,7 @@ soupsieve==2.3.2
 stack-data==0.5.0
 terminado==0.15.0
 testpath==0.6.0
-tornado==6.4.1
+tornado==6.4.2
 traitlets==5.3.0
 urllib3==1.26.19
 wcwidth==0.2.5