fix import of parse_requirements for pip v10

[jimmyland]

currently with the latest pip, setup fails with "ImportError: No module named req"
This fix is via: https://stackoverflow.com/questions/25192794/no-module-named-pip-req

[raffienficiaud]

Please bump the version as well and merge this, we are having a lot of troubles with the new students 😀

[BenjaminAllain]

Ideally, the internal pip APIs should not be called by external code. The pip development team moved pip.req to pip._internal.req in order to make this explicit.

Yet I think this PR should be merged (as a hotfix) because the current state is broken with pip version 10.

sources:
https://groups.google.com/forum/#!topic/pypa-dev/JVTfS6ZdAuM
https://pip.pypa.io/en/latest/user_guide/#using-pip-from-your-program

[Rubikplayer]

Hey guys, shall we merge this PR for fixing pip v10 installation issue?