Bump tornado from 6.5.2 to 6.5.5

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.5.2 to 6.5.5.
- [Changelog](https://github.com/tornadoweb/tornado/blob/master/docs/releases.rst)
- [Commits](tornadoweb/tornado@v6.5.2...v6.5.5)

---
updated-dependencies:
- dependency-name: tornado
  dependency-version: 6.5.5
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements.txt

@@ -197,7 +197,7 @@ terminado==0.18.1
     #   jupyter-server-terminals
 tinycss2==1.4.0
     # via bleach
-tornado==6.5.2
+tornado==6.5.5
     # via
     #   -r requirements.in
     #   jupyter-client