Fix the build

[lupino3]

Unit tests are failing, but the recent changes only touch README.md.

The error is the following:

2019-01-06T17:35:53.2926467Z =================================== FAILURES ===================================
2019-01-06T17:35:53.2930569Z ______________________ CodeLineTest.test_command_counters ______________________
2019-01-06T17:35:53.2933899Z 
2019-01-06T17:35:53.2940444Z self = <pytest_cov.plugin.CovPlugin object at 0x7f336dc97cd0>
2019-01-06T17:35:53.2950537Z item = <TestCaseFunction test_command_counters>
2019-01-06T17:35:53.2957731Z 
2019-01-06T17:35:53.2958299Z     @compat.hookwrapper
2019-01-06T17:35:53.2973012Z     def pytest_runtest_call(self, item):
2019-01-06T17:35:53.2989594Z >       if (item.get_marker('no_cover')
2019-01-06T17:35:53.2990087Z                 or 'no_cover' in getattr(item, 'fixturenames', ())):
2019-01-06T17:35:53.2990448Z E               AttributeError: 'TestCaseFunction' object has no attribute 'get_marker'

This seems to be related to a very recent change in pytest. From https://docs.pytest.org/en/latest/changelog.html#pytest-4-1-0-2019-01-05:

#4546: Remove Node.get_marker(name) the return value was not usable for more than a existence check. - pytest-dev/pytest#4546

[lupino3]

Unit tests are now passing, thanks to a new release of pytest-cov which doesn't use the removed method.