Bump pip version to 9.0.1

[ye]

$ docker pull python:3.5
3.5: Pulling from library/python
386a066cd84a: Pull complete 
75ea84187083: Pull complete 
88b459c9f665: Pull complete 
1e3ee139a577: Pull complete 
729baab2cba2: Pull complete 
6792e43546b2: Pull complete 
61cd79806d9e: Pull complete 
Digest: sha256:845576d452e927e6d72502daf2f0e328b2464b56818786533dbcf18d42ccd827
Status: Downloaded newer image for python:3.5

$ docker run --rm -it python:3.5 bash
root@11b136f8b106:/# pip -V
pip 8.1.2 from /usr/local/lib/python3.5/site-packages (python 3.5)

root@11b136f8b106:/# pip install six
Collecting six
  Downloading six-1.10.0-py2.py3-none-any.whl
Installing collected packages: six
Successfully installed six-1.10.0
You are using pip version 8.1.2, however version 9.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

root@11b136f8b106:/# pip install --upgrade pip
Collecting pip
  Downloading pip-9.0.1-py2.py3-none-any.whl (1.3MB)
    100% |████████████████████████████████| 1.3MB 1.1MB/s 
Installing collected packages: pip
  Found existing installation: pip 8.1.2
    Uninstalling pip-8.1.2:
      Successfully uninstalled pip-8.1.2
Successfully installed pip-9.0.1

[ye]

Oops, looks like a dupe of #154