pip 9.0 is out

[snippsat]

Release Notes

Release features:

• The 9.x series will be the last pip versions to support Python 2.6.
  
• Support for Requires-Python (will require additional support in setuptools/PyPI)
  to allow releasing sdists that will be ignored by specific versions of Python (e.g. foobar 5.x doesn’t get downloaded on 2.6).
  
• Ability to pass platform, Python version, implementation, etc into pip download to download wheels for other platforms.
  
• Add a pick check command to check the state of installed dependencies.
  
• Add new formats for pip list, including a new columnar layout and a JSON format for ease of scripting.