Update urllib3 to 1.26.8

[pyup-bot]

This PR updates urllib3 from 1.26.6 to 1.26.8.

Changelog

1.26.7

===================

* Fixed a bug with HTTPS hostname verification involving IP addresses and lack
of SNI. (Issue 2400)
* Fixed a bug where IPv6 braces weren't stripped during certificate hostname
matching. (Issue 2240)

Links

• PyPI: https://pypi.org/project/urllib3
• Changelog: https://pyup.io/changelogs/urllib3/
• Docs: https://urllib3.readthedocs.io/

[pyup-bot]

Closing this in favor of #405