Bump tornado from 6.5.6 to 6.5.7 (#29)

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.5.6 to 6.5.7.
- [Changelog](https://github.com/tornadoweb/tornado/blob/master/docs/releases.rst)
- [Commits](tornadoweb/tornado@v6.5.6...v6.5.7)

---
updated-dependencies:
- dependency-name: tornado
  dependency-version: 6.5.7
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,3 +1,3 @@
 beautifulsoup4==4.6.0
 chardet==3.0.4
-tornado==6.5.6
+tornado==6.5.7