After installing virtual Environment pip version is downgraded from 18.1 to 7.1.2.
This leads to a UserWarning: Unknown distribution option: 'python_requires' because 'python_requires' was introduced with pip 9.0
See https://ci.appveyor.com/project/Ladsgroup/pywikibot-g4xqx/builds/22838345/job/pntk4yapsh4bf2kn