flaky broken with pytest 4.1

[gaborbernat]

pytest-dev/pytest#4299 breaks https://github.com/box/flaky/blob/master/flaky/flaky_pytest_plugin.py#L272 cc @RonnyPfannschmidt

INTERNALERROR>     call = self.call_runtest_hook(item, when, **kwds)
INTERNALERROR>   File ".tox/dev/lib/python3.7/site-packages/flaky/flaky_pytest_plugin.py", line 274, in call_runtest_hook
INTERNALERROR>     when=when,
INTERNALERROR> TypeError: __init__() missing 3 required positional arguments: 'excinfo', 'start', and 'stop'

[bwindsor22]

If you're arriving here from the future:
pip install --upgrade flaky

Thanks for all you do folks!