devel/py-flex: Update to 6.14.0

While I'm here:

• Pet portlint

Changelog:

• Allow space in mimetype before parameters
• Open up dependency requirements
• Increased test coverage with additional vectors, rearranged
• Fixed warning about importing from collections on Python 3

https://github.com/pipermerriam/flex/releases/tag/v6.14.0

Approved by: mentors (implicit)