Update urllib3 to 1.24

[pyup-bot]

This PR updates urllib3 from 1.23 to 1.24.

Changelog

1.24

-----------------

* Allow key_server_hostname to be specified when initializing a PoolManager to allow custom SNI to be overridden. (Pull 1449)

* Test against Python 3.7 on AppVeyor. (Pull 1453)

* Early-out ipv6 checks when running on App Engine. (Pull 1450)

* Change ambiguous description of backoff_factor (Pull 1436)

* Add ability to handle multiple Content-Encodings (Issue 1441 and Pull 1442)

* Skip DNS names that can't be idna-decoded when using pyOpenSSL (Issue 1405).

* Add a server_hostname parameter to HTTPSConnection which allows for
overriding the SNI hostname sent in the handshake. (Pull 1397)

* Drop support for EOL Python 2.6 (Pull 1429 and Pull 1430)

* Fixed bug where responses with header Content-Type: message/* erroneously
raised HeaderParsingError, resulting in a warning being logged. (Pull 1439)

* Move urllib3 to src/urllib3 (Pull 1409)

Links

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

[glasserc]

Blocked on psf/requests#4830.

[glasserc]

Rebased onto master now that #1830 has landed. This should unblock this.