Update cryptography to 1.7.2

[pyup-bot]

There's a new version of cryptography available.
You are currently using 1.6. I have updated it to 1.7.2

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

Changelog

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 #16