Updated py-cryptography to 1.6.

1.6 - 2016-11-22
~~~~~~~~~~~~~~~~

* Deprecated support for OpenSSL 1.0.0. Support will be removed in
  ``cryptography`` 1.7.
* Replaced the Python-based OpenSSL locking callbacks with a C version to fix
  a potential deadlock that could occur if a garbage collection cycle occurred
  while inside the lock.
* Added support for :class:`~cryptography.hazmat.primitives.hashes.BLAKE2b` and
  :class:`~cryptography.hazmat.primitives.hashes.BLAKE2s` when using OpenSSL
  1.1.0.
* Added
  :attr:`~cryptography.x509.Certificate.signature_algorithm_oid` support to
  :class:`~cryptography.x509.Certificate`.
* Added
  :attr:`~cryptography.x509.CertificateSigningRequest.signature_algorithm_oid`
  support to :class:`~cryptography.x509.CertificateSigningRequest`.
* Added
  :attr:`~cryptography.x509.CertificateRevocationList.signature_algorithm_oid`
  support to :class:`~cryptography.x509.CertificateRevocationList`.
* Added support for :class:`~cryptography.hazmat.primitives.kdf.scrypt.Scrypt`
  when using OpenSSL 1.1.0.
* Added a workaround to improve compatibility with Python application bundling
  tools like ``PyInstaller`` and ``cx_freeze``.
* Added support for generating a
  :meth:`~cryptography.x509.random_serial_number`.
* Added support for encoding ``IPv4Network`` and ``IPv6Network`` in X.509
  certificates for use with :class:`~cryptography.x509.NameConstraints`.
* Added :meth:`~cryptography.x509.Name.public_bytes` to
  :class:`~cryptography.x509.Name`.
* Added :class:`~cryptography.x509.RelativeDistinguishedName`
* :class:`~cryptography.x509.DistributionPoint` now accepts
  :class:`~cryptography.x509.RelativeDistinguishedName` for
  :attr:`~cryptography.x509.DistributionPoint.relative_name`.
  Deprecated use of :class:`~cryptography.x509.Name` as
  :attr:`~cryptography.x509.DistributionPoint.relative_name`.
* :class:`~cryptography.x509.Name` now accepts an iterable of
  :class:`~cryptography.x509.RelativeDistinguishedName`.  RDNs can
  be accessed via the :attr:`~cryptography.x509.Name.rdns`
  attribute.  When constructed with an iterable of
  :class:`~cryptography.x509.NameAttribute`, each attribute becomes
  a single-valued RDN.
* Added
  :func:`~cryptography.hazmat.primitives.asymmetric.ec.derive_private_key`.
* Added support for signing and verifying RSA, DSA, and ECDSA signatures with
  :class:`~cryptography.hazmat.primitives.asymmetric.utils.Prehashed`
  digests.

(wiz)