Bump urllib3 from 1.24.2 to 1.26.5 in /docs

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.24.2 to 1.26.5.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@1.24.2...1.26.5)

---
updated-dependencies:
- dependency-name: urllib3
  dependency-type: direct:production
...

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

docs/requirements.txt

@@ -87,7 +87,7 @@ testpath==0.4.2
 tornado==6.0.2
 traitlets==4.3.2
 traittypes==0.2.1
-urllib3==1.24.2
+urllib3==1.26.5
 wcwidth==0.1.7
 webencodings==0.5.1
 widgetsnbextension==3.4.2