Update cryptography to 3.1

[pyup-bot]

This PR updates cryptography from 3.0 to 3.1.

Changelog

3.1

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

* **BACKWARDS INCOMPATIBLE:** Removed support for ``idna`` based
:term:`U-label` parsing in various X.509 classes. This support was originally
deprecated in version 2.1 and moved to an extra in 2.5.
* Deprecated OpenSSL 1.0.2 support. OpenSSL 1.0.2 is no longer supported by
the OpenSSL project. The next version of ``cryptography`` will drop support
for it.
* Deprecated support for Python 3.5. This version sees very little use and will
be removed in the next release.
* ``backend`` arguments to functions are no longer required and the
default backend will automatically be selected if no ``backend`` is provided.
* Added initial support for parsing certificates from PKCS7 files with
:func:`~cryptography.hazmat.primitives.serialization.pkcs7.load_pem_pkcs7_certificates`
and
:func:`~cryptography.hazmat.primitives.serialization.pkcs7.load_der_pkcs7_certificates`
.
* Calling ``update`` or ``update_into`` on
:class:`~cryptography.hazmat.primitives.ciphers.CipherContext` with ``data``
longer than 2\ :sup:`31` bytes no longer raises an ``OverflowError``. This
also resolves the same issue in :doc:`/fernet`.

.. _v3-0:

Links

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

[coveralls]

Coverage remained the same at 76.186% when pulling 4560c4f on pyup-update-cryptography-3.0-to-3.1 into 26f5e53 on master.