Log Message:
Updated py-cryptography to 1.8.1.

1.8.1 - 2017-03-10
~~~~~~~~~~~~~~~~~~

* Fixed macOS wheels to properly link against 1.1.0 rather than 1.0.2.

1.8 - 2017-03-09
~~~~~~~~~~~~~~~~

* Added support for Python 3.6.
* Windows and macOS wheels now link against OpenSSL 1.1.0.
* macOS wheels are no longer universal. This change significantly shrinks the
  size of the wheels. Users on macOS 32-bit Python (if there are any) should
  migrate to 64-bit or build their own packages.
* Changed ASN.1 dependency from ``pyasn1`` to ``asn1crypto`` resulting in a
  general performance increase when encoding/decoding ASN.1 structures. Also,
  the ``pyasn1_modules`` test dependency is no longer required.
* Added support for
  :meth:`~cryptography.hazmat.primitives.ciphers.CipherContext.update_into` on
  :class:`~cryptography.hazmat.primitives.ciphers.CipherContext`.
* Added
  \ 
:meth:`~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateKeyWithSerializati \ 
on.private_bytes`
  to
  \ 
:class:`~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateKeyWithSerializat \ 
ion`.
* Added
  \ 
:meth:`~cryptography.hazmat.primitives.asymmetric.dh.DHPublicKeyWithSerializatio \ 
n.public_bytes`
  to
  \ 
:class:`~cryptography.hazmat.primitives.asymmetric.dh.DHPublicKeyWithSerializati \ 
on`.
* :func:`~cryptography.hazmat.primitives.serialization.load_pem_private_key`
  and
  :func:`~cryptography.hazmat.primitives.serialization.load_der_private_key`
  now require that ``password`` must be bytes if provided. Previously this
  was documented but not enforced.
* Added support for subgroup order in :doc:`/hazmat/primitives/asymmetric/dh`.