Update cryptography to 1.8.1

[pyup-bot]

There's a new version of cryptography available.
You are currently using 1.6. I have updated it to 1.8.1

These links might come in handy: PyPI | Changelog | Repo

Changelog

1.8

• 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.DHPrivateKeyWithSerialization.private_bytes
  to
  :class:~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateKeyWithSerialization.
• Added
  :meth:~cryptography.hazmat.primitives.asymmetric.dh.DHPublicKeyWithSerialization.public_bytes
  to
  :class:~cryptography.hazmat.primitives.asymmetric.dh.DHPublicKeyWithSerialization.
• :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.

1.7.2

• Updated Windows and macOS wheels to be compiled against OpenSSL 1.0.2k.

1.7.1

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

1.7

• 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>_.

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖

[pyup-bot]

Closing this in favor of #27