Update gitpython to 3.1.9

[pyup-bot]

This PR updates gitpython from 3.1.7 to 3.1.9.

Changelog

3.1.9

=====

See the following for details:
https://github.com/gitpython-developers/gitpython/milestone/41?closed=1*

3.1.8

=====

* support for 'includeIf' in git configuration files
* tests are now excluded from the package, making it conisderably smaller


See the following for more details:
https://github.com/gitpython-developers/gitpython/milestone/40?closed=1*

Links

• PyPI: https://pypi.org/project/gitpython
• Changelog: https://pyup.io/changelogs/gitpython/
• Repo: https://github.com/gitpython-developers/GitPython
• Docs: https://pythonhosted.org/GitPython/

[pyup-bot]

Closing this in favor of #54