Fix compat with pytest 5.x

[rpkilby]

The following is preventing compatibility with the newly release pytest 5.0:

pytest.PytestDeprecationWarning: The `funcargnames` attribute was an alias for `fixturenames`, since pytest 2.3 - use the newer attribute instead.

[rpkilby]

Note that pytest 5.x has dropped py27 and py34 support, although, the related builds seem to be passing. I'm assuming that pytest-django is just not hitting those code paths where pytest would otherwise fail.

Eitherway, this should be safe to merge, since the changes have been deprecated since pytest 2.3

[blueyed]

Note that pytest 5.x has dropped py27 and py34 support, although, the related builds seem to be passing. I'm assuming that pytest-django is just not hitting those code paths where pytest would otherwise fail.

It is using pytest 4.6 there.