Upgrade pytest to re-enable hypothesis

[carver]

What was wrong?

/home/jcarver/code/eth-keys/venv/lib/python3.6/site-packages/hypothesis/extra/pytestplugin.py:61: HypothesisWarning: 
        You are using Pytest version 3.2.2.  Hypothesis tests work with any test
        runner, but our Pytest plugin requires Pytest  4.3 or newer.
        Note that the Pytest developers no longer support this version either!
        Disabling the Hypothesis pytest plugin...
    
  warnings.warn(PYTEST_TOO_OLD_MESSAGE % (pytest.__version__,), HypothesisWarning)

How can it be fixed?

Upgrade pytest. Should be very easy, just juggling a few other things right now.