Update cryptography to 2.4.2

[pyup-bot]

This PR updates cryptography from 2.3.1 to 2.4.2.

Changelog

2.4.1

~~~~~~~~~~~~~~~~~~

* Fixed a build breakage in our ``manylinux1`` wheels.

.. _v2-4:

2.4

~~~~~~~~~~~~~~~~

* **BACKWARDS INCOMPATIBLE:** Dropped support for LibreSSL 2.4.x.
* Deprecated OpenSSL 1.0.1 support. OpenSSL 1.0.1 is no longer supported by
the OpenSSL project. At this time there is no time table for dropping
support, however we strongly encourage all users to upgrade or install
``cryptography`` from a wheel.
* Added initial :doc:`OCSP </x509/ocsp>` support.
* Added support for :class:`~cryptography.x509.PrecertPoison`.

.. _v2-3-1:

Links

• PyPI: https://pypi.org/project/cryptography
• Changelog: https://pyup.io/changelogs/cryptography/
• Repo: https://github.com/pyca/cryptography

[pyup-bot]

Closing this in favor of #195