Bump tornado in /research/information_retrieval/doc2query

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.3.2 to 6.4.1.
- [Changelog](https://github.com/tornadoweb/tornado/blob/master/docs/releases.rst)
- [Commits](tornadoweb/tornado@v6.3.2...v6.4.1)

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

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

research/information_retrieval/doc2query/requirements.txt

@@ -121,7 +121,7 @@ tifffile==2021.6.14
 tokenizers==0.10.3
 toposort==1.6
 torch==1.8.0
-tornado==6.3.2
+tornado==6.4.1
 tqdm==4.61.1
 traitlets==5.0.5
 transformers==4.7.0