Update urllib3 to 1.25.6

[pyup-bot]

This PR updates urllib3 from 1.25.3 to 1.25.6.

Changelog

1.25.6

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

* Fix issue where tilde (``~``) characters were incorrectly
percent-encoded in the path. (Pull 1692)

1.25.5

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

* Add mitigation for BPO-37428 affecting Python <3.7.4 and OpenSSL 1.1.1+ which
caused certificate verification to be enabled when using ``cert_reqs=CERT_NONE``.
(Issue 1682)

1.25.4

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

* Propagate Retry-After header settings to subsequent retries. (Pull 1607)

* Fix edge case where Retry-After header was still respected even when
explicitly opted out of. (Pull 1607)

* Remove dependency on ``rfc3986`` for URL parsing.

* Fix issue where URLs containing invalid characters within ``Url.auth`` would
raise an exception instead of percent-encoding those characters.

* Add support for ``HTTPResponse.auto_close = False`` which makes HTTP responses
work well with BufferedReaders and other ``io`` module features. (Pull 1652)

* Percent-encode invalid characters in URL for ``HTTPConnectionPool.request()`` (Pull 1673)

Links

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