Setup doesn't work with latest pip version

[charlesollion]

try:  # for pip >= 10
    from pip._internal.req import parse_requirements
    from pip._internal.download import PipSession
except ImportError:  # for pip <= 9.0.3
    from pip.req import parse_requirements
    from pip.download import PipSession

fails with pip 20.0.2

This usage of pip is not the right one according to pypa/pip#7645

[EmGarr]

It has been fixed in the commit: 06bf1e7