this version is needed for obs-service-python_requires to work

- update to 16.8:
* Fix markers that utilize ``in`` so that they render correctly.
* Fix an erroneous test on Python RC releases.

- update to 16.7:
* Add support for the deprecated ``python_implementation`` marker which was
an undocumented setuptools marker in addition to the newer markers.
* Add support for the deprecated, PEP 345 environment markers in addition to
the newer markers.

- update to 16.5:
* Fix a regression in parsing requirements with whitespaces between the comma
separators.
* Fix a regression in parsing requirements like ``foo (==4)``.
* Fix a bug where ``packaging.requirements:Requirement`` was overly strict when
matching legacy requirements.
* Add a function that implements the name canonicalization from PEP 503.
* Implement requirement specifiers from PEP 508.
* Relicense so that packaging is available under *either* the Apache License,
Version 2.0 or a 2 Clause BSD license.
* Support installation of packaging when only distutils is available.
* Fix ``==`` comparison when there is a prefix and a local version in play.
(:issue:`41`).
* Implement environment markers from PEP 508.
- Adjust Requires according to requires.txt

- update to 15.3:
* Normalize post-release spellings for rev/r prefixes. :issue:`35`