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] <[email protected]>

Author: dependabot[bot]

docs/requirements.txt

@@ -5,6 +5,6 @@ future==0.16.0
 idna==2.7
 requests==2.20.0
 six==1.11.0
-urllib3==1.24.2
+urllib3==1.26.5
 pytest==3.6.1
 daraja-mpesa