py-packaging: updated to 17.1

17.1:
Fix utils.canonicalize_version when supplying non PEP 440 versions.

17.0:
Drop support for python 2.6, 3.2, and 3.3.
Define minimal pyparsing version to 2.0.2.
Add epoch, release, pre, dev, and post attributes to Version and LegacyVersion.
Add Version().is_devrelease and LegacyVersion().is_devrelease to make it easy to determine if a release is a development release.
Add utils.canonicalize_version to canonicalize version strings or Version instances

(adam)