Incompatibilty with Pytest 4.1.0

[Craig Blaszczyk]

item = <TestCaseFunction test_get_events_by_policy>
    def pytest_runtest_setup(item):
>       if not item.get_marker('withoutresponses'):
E       AttributeError: 'TestCaseFunction' object has no attribute 'get_marker'
../../../.cache/tox/app/lib/python3.6/site-packages/pytest_responses.py:8: AttributeError

get_marker has been removed in pytest 4.1.0The pytest changelog suggests using get_closest_marker instead.

https://docs.pytest.org/en/latest/changelog.html

[Justin Menga]

This should be fixed by #7

[Craig Blaszczyk]

@dcramer Does this PR look ok to you?

[Wes Kendall]

@dcramer can #9 be released? Should be able to close this issue

[David Cramer]

Pushing out 0.4.0