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

@@ -74,7 +74,7 @@ txaio==2.5.1
 txdbus==1.0.13
 txmsgpackrpc==1.1
 typing==3.6.2
-urllib3==1.24.2
+urllib3==1.26.5
 websocket-client==0.37.0
 Werkzeug==0.12.2
 wget==3.2