build(deps): bump tornado in /images/singleuser-sample

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.3.1 to 6.3.2.
- [Changelog](https://github.com/tornadoweb/tornado/blob/master/docs/releases.rst)
- [Commits](tornadoweb/tornado@v6.3.1...v6.3.2)

---
updated-dependencies:
- dependency-name: tornado
  dependency-type: indirect
...

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

Author: dependabot[bot]

images/singleuser-sample/requirements.txt

@@ -309,7 +309,7 @@ terminado==0.17.1
     #   notebook
 tinycss2==1.2.1
     # via nbconvert
-tornado==6.3.1
+tornado==6.3.2
     # via
     #   ipykernel
     #   jupyter-client