Log Message:
Update py-cryptography to 1.3.1.

1.3.1 - 2016-03-21
~~~~~~~~~~~~~~~~~~

* Fixed a bug that caused an ``AttributeError`` when using ``mock`` to patch
  some ``cryptography`` modules.

1.3 - 2016-03-18
~~~~~~~~~~~~~~~~

* Added support for padding ANSI X.923 with
  :class:`~cryptography.hazmat.primitives.padding.ANSIX923`.
* Deprecated support for OpenSSL 0.9.8. Support will be removed in
  ``cryptography`` 1.4.
* Added support for the :class:`~cryptography.x509.PolicyConstraints`
  X.509 extension including both parsing and generation using
  :class:`~cryptography.x509.CertificateBuilder` and
  :class:`~cryptography.x509.CertificateSigningRequestBuilder`.
* Added :attr:`~cryptography.x509.CertificateSigningRequest.is_signature_valid`
  to :class:`~cryptography.x509.CertificateSigningRequest`.
* Fixed an intermittent ``AssertionError`` when performing an RSA decryption on
  an invalid ciphertext, ``ValueError`` is now correctly raised in all cases.
* Added
  \ 
:meth:`~cryptography.x509.AuthorityKeyIdentifier.from_issuer_subject_key_identif \ 
ier`.