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

@@ -172,7 +172,7 @@ threadpoolctl @ file:///tmp/tmp79xdzxkt/threadpoolctl-2.1.0-py3-none-any.whl
 tifffile @ file:///home/conda/feedstock_root/build_artifacts/tifffile_1595673894086/work
 toml==0.10.1
 toolz==0.10.0
-tornado==6.4.1
+tornado==6.4.2
 tqdm @ file:///home/conda/feedstock_root/build_artifacts/tqdm_1596476591553/work
 traitlets==4.3.3
 typed-ast==1.4.1