Try to import parse_requirements from pip._internal.req too.

[fhahn]

Summary

Pip's internal modules have been moved to pip._internal in
95bcf8c5f6394298035a7332c441868f3b0169f4 [1], which is part of the 10.0.0b2
release.

[1] https://github.com/pypa/pip/commit/95bcf8c5f6394298035a7332c441868f3b0169f4

[cmatthews]

LGTM.

[MatzeB]

Should we maybe move the requirement list into setup.py instead of using this functionality which they apparently don't want us to use like this? (I'm fine with this patch in the meantime)

[cmatthews]

The requirements file is needed for Heroku like clouds support.

setup.py

+try:
     from pip.req import parse_requirements
+except ImportError:
+    # The req module has been moved to pip._internal in the 10 release.
+    from pip._internal.req import parse_requirements
 import lnt
 import os
 from sys import platform as _platform
 import sys
 from setuptools import setup, find_packages, Extension
 
 cflags = []