Update bump2version to 0.5.11

[pyup-bot]

This PR updates bump2version from 0.5.10 to 0.5.11.

Changelog

0.5.11

- Housekeeping, also publish an sdist
- Housekeeping, fix appveyor builds
- Housekeeping, `make lint` now lints with pylint
- Drop support for Python3.4, thanks hugovk 79 
- Enhance missing VCS command detection (errno 13), thanks lowell80 75
- Add environment variables for other scripts to use, thanks mauvilsa 70
- Refactor, cli.main is now much more readable, thanks florisla 68
- Fix, retain file newlines for Windows, thanks hesstobi 59
- Add support (tests) for Pythno3.7, thanks florisla 49
- Allow any part to be configured in configurable strings such as tag_name etc., thanks florisla 41

Links

• PyPI: https://pypi.org/project/bump2version
• Changelog: https://pyup.io/changelogs/bump2version/
• Repo: https://github.com/c4urself/bump2version