Update lowest required pytest version

[sliwinski-milosz]

We use bool type ini option for bdd_strict_gherkin.

Support for that type has been added to Parser.addini starting from pytest==2.9.0.
https://docs.pytest.org/en/latest/changelog.html#id625

Due to above pytest==2.9.0 is the lowest version that latest pytest-bdd can work with.

For testing with pytest==2.9.0 you have to use pytest-xdist<=1.17 as newer pytest-xdist requires pytest>=3.0.0.

[coveralls]

Coverage remained the same at 93.363% when pulling 30eb6a5 on sliwinski-milosz:update_lowest_required_pytest into 9dd326a on pytest-dev:master.

[youtux]

Makes sense. I think we don't need a major version bump, since the compatibility with pytest<2.9.0 has been broken in pytest-bdd 3.0.0.
Can you also bump the version to of pytest-bdd to 3.0.1 and add an entry in the changelog?

[youtux]

Thank you again @sliwinski-milosz :)