Bump tornado from 6.3.3 to 6.4.1 in /examples (#1376)

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.3.3 to 6.4.1.
- [Changelog](https://github.com/tornadoweb/tornado/blob/master/docs/releases.rst)
- [Commits](tornadoweb/tornado@v6.3.3...v6.4.1)

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

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

examples/requirements.txt

@@ -44,7 +44,7 @@ six==1.16.0
 soupsieve==2.3.2.post1
 stack-data==0.4.0
 tinycss2==1.1.1
-tornado==6.3.3
+tornado==6.4.1
 traitlets==5.3.0
 wcwidth==0.2.5
 webencodings==0.5.1