Update cryptography to 2.8

[pyup-bot]

This PR updates cryptography from 2.7 to 2.8.

Changelog

2.8

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

* Updated Windows, macOS, and ``manylinux1`` wheels to be compiled with
OpenSSL 1.1.1d.
* Added support for Python 3.8.
* Added class methods
:meth:`Poly1305.generate_tag
<cryptography.hazmat.primitives.poly1305.Poly1305.generate_tag>`
and
:meth:`Poly1305.verify_tag
<cryptography.hazmat.primitives.poly1305.Poly1305.verify_tag>`
for Poly1305 sign and verify operations.
* Deprecated support for OpenSSL 1.0.1. Support will be removed in
``cryptography`` 2.9.
* We now ship ``manylinux2010`` wheels in addition to our ``manylinux1``
wheels.
* Added support for ``ed25519`` and ``ed448`` keys in the
:class:`~cryptography.x509.CertificateBuilder`,
:class:`~cryptography.x509.CertificateSigningRequestBuilder`,
:class:`~cryptography.x509.CertificateRevocationListBuilder` and
:class:`~cryptography.x509.ocsp.OCSPResponseBuilder`.
* ``cryptography`` no longer depends on ``asn1crypto``.
* :class:`~cryptography.x509.FreshestCRL` is now allowed as a
:class:`~cryptography.x509.CertificateRevocationList` extension.

.. _v2-7:

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 #293