fix: pip 10 compatibility (clemfromspace#12)

Author: leon0707

setup.py

@@ -1,8 +1,14 @@
 """This module contains the packaging routine for the pybook package"""
 
 from setuptools import setup, find_packages
-from pip.download import PipSession
-from pip.req import parse_requirements
+try:
+    from pip.download import PipSession
+    from pip.req import parse_requirements
+except ImportError:
+    # It is quick hack to support pip 10 that has changed its internal
+    # structure of the modules.
+    from pip._internal.download import PipSession
+    from pip._internal.req.req_file import parse_requirements
 
 
 def get_requirements(source):