Update flex to 6.14.1

[pyup-bot]

This PR updates flex from 6.13.2 to 6.14.1.

Changelog

6.14.1

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- Fixed all warnings about importing from collections on Python 3
(thanks to sloria)
https://github.com/pipermerriam/flex/pull/222

6.14.0

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- Allow space in mimetype before parameters (thanks to miki725)
https://github.com/pipermerriam/flex/pull/206
- Open up dependency requirements (thanks to blueyed, javabrett)
https://github.com/pipermerriam/flex/pull/207
https://github.com/pipermerriam/flex/pull/211
- Increased test coverage with additional vectors, rearranged tests
https://github.com/pipermerriam/flex/pull/214
https://github.com/pipermerriam/flex/pull/216
- Fixed warning about importing from collections on Python 3 (thanks to sloria)
https://github.com/pipermerriam/flex/pull/215

Links

• PyPI: https://pypi.org/project/flex
• Changelog: https://pyup.io/changelogs/flex/
• Repo: https://github.com/pipermerriam/flex