Updated py-cryptography to 1.7.1.

1.7.1 - 2016-12-13
~~~~~~~~~~~~~~~~~~

* Fixed a regression in ``int_from_bytes`` where it failed to accept
  ``bytearray``.

1.7 - 2016-12-12
~~~~~~~~~~~~~~~~

* Support for OpenSSL 1.0.0 has been removed. Users on older version of OpenSSL
  will need to upgrade.
* Added support for Diffie-Hellman key exchange using
  :meth:`~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateKeyWithSerialization.exchange`
* The OS random engine for OpenSSL has been rewritten to improve compatibility
  with embedded Python and other edge cases. More information about this change
  can be found in the
  `pull request <https://github.com/pyca/cryptography/pull/3229>`_.

(wiz)