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
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

requirements_with_versions.txt

@@ -37,7 +37,7 @@ xlrd==2.0.1
 fpdf==1.7.2
 mysql-connector-repackaged==0.3.1
 word2number==1.1
-tornado==6.4.1
+tornado==6.4.2
 obs==0.0.0
 todo==0.1
 oauth2client==4.1.3