Bump tornado from 4.5.3 to 6.4.2 in /frameworks/Python/bottle

Bumps [tornado](https://github.com/tornadoweb/tornado) from 4.5.3 to 6.4.2.
- [Changelog](https://github.com/tornadoweb/tornado/blob/v6.4.2/docs/releases.rst)
- [Commits](https://github.com/tornadoweb/tornado/compare/v4.5.3...v6.4.2)

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

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

frameworks/Python/bottle/requirements-pypy.txt

@@ -3,4 +3,4 @@ bottle-sqlalchemy==0.4.3
 gunicorn==19.9.0
 PyMySQL==0.8.0
 SQLAlchemy==1.3.0
-tornado==4.5.3
+tornado==6.4.2