Bump urllib3 from 1.21.1 to 1.26.5

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.21.1 to 1.26.5.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](https://github.com/urllib3/urllib3/compare/1.21.1...1.26.5)

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

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

requirements.txt

@@ -8,4 +8,4 @@ pytz==2017.2
 requests==2.17.3
 six==1.10.0
 twilio==6.3.0
-urllib3==1.21.1
+urllib3==1.26.5