Update cryptography to 2.9.1

[pyup-bot]

This PR updates cryptography from 2.8 to 2.9.1.

Changelog

2.9

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

* **BACKWARDS INCOMPATIBLE:** Support for Python 3.4 has been removed due to
low usage and maintenance burden.
* **BACKWARDS INCOMPATIBLE:** Support for OpenSSL 1.0.1 has been removed.
Users on older version of OpenSSL will need to upgrade.
* **BACKWARDS INCOMPATIBLE:** Support for LibreSSL 2.6.x has been removed.
* Removed support for calling
:meth:`~cryptography.hazmat.primitives.asymmetric.x25519.X25519PublicKey.public_bytes`
with no arguments, as per our deprecation policy. You must now pass
``encoding`` and ``format``.
* **BACKWARDS INCOMPATIBLE:** Reversed the order in which
:meth:`~cryptography.x509.Name.rfc4514_string` returns the RDNs
as required by :rfc:`4514`.
* Updated Windows, macOS, and ``manylinux`` wheels to be compiled with
OpenSSL 1.1.1f.
* Added support for parsing
:attr:`~cryptography.x509.ocsp.OCSPResponse.single_extensions` in an OCSP
response.
* :class:`~cryptography.x509.NameAttribute` values can now be empty strings.

.. _v2-8:

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 42.065% when pulling 69f10ae on pyup-update-cryptography-2.8-to-2.9.1 into 10a4d82 on master.

[pyup-bot]

Closing this in favor of #407