Update cryptography to 2.4.1

[pyup-bot]

This PR updates cryptography from 2.3.1 to 2.4.1.

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

[codecov-io]

Codecov Report

Merging #338 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #338   +/-   ##
=======================================
  Coverage   36.13%   36.13%           
=======================================
  Files          30       30           
  Lines        3025     3025           
=======================================
  Hits         1093     1093           
  Misses       1932     1932

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[pyup-bot]

Closing this in favor of #350