Update gitpython to 3.1.0

[pyup-bot]

This PR updates GitPython from 2.1.14 to 3.1.0.

Changelog

3.1.0

=====

* Switched back to using gitdb package as requirement
(`gitdb59 <https://github.com/gitpython-developers/gitdb/issues/59>`_)

3.0.9

=====

* Restricted GitDB (gitdb2) version requirement to < 4
* Removed old nose library from test requirements

Bugfixes
--------

* Changed to use UTF-8 instead of default encoding when getting information about a symbolic reference
(`774 <https://github.com/gitpython-developers/GitPython/issues/774>`_)
* Fixed decoding of tag object message so as to replace invalid bytes
(`943 <https://github.com/gitpython-developers/GitPython/issues/943>`_)

3.0.8

=====

* Added support for Python 3.8
* Bumped GitDB (gitdb2) version requirement to > 3

Bugfixes
--------

* Fixed Repo.__repr__ when subclassed 
(`968 <https://github.com/gitpython-developers/GitPython/pull/968>`_)
* Removed compatibility shims for Python < 3.4 and old mock library
* Replaced usage of deprecated unittest aliases and Logger.warn
* Removed old, no longer used assert methods
* Replaced usage of nose assert methods with unittest

3.0.7

=====

Properly signed re-release of v3.0.6 with new signature
(See `980 <https://github.com/gitpython-developers/GitPython/issues/980>`_)

3.0.6

=====

| Note: There was an issue that caused this version to be released to PyPI without a signature
| See the changelog for v3.0.7 and `980 <https://github.com/gitpython-developers/GitPython/issues/980>`_

Bugfixes
--------

* Fixed warning for usage of environment variables for paths containing ``$`` or ``%``
(`832 <https://github.com/gitpython-developers/GitPython/issues/832>`_, 
`961 <https://github.com/gitpython-developers/GitPython/pull/961>`_)
* Added support for parsing Git internal date format (<unix timestamp> <timezone offset>)
(`965 <https://github.com/gitpython-developers/GitPython/pull/965>`_)
* Removed Python 2 and < 3.3 compatibility shims
(`979 <https://github.com/gitpython-developers/GitPython/pull/965>`_)
* Fixed GitDB (gitdb2) requirement version specifier formatting in requirements.txt
(`979 <https://github.com/gitpython-developers/GitPython/pull/965>`_)

3.0.5

=============================================

see the following for details:
https://github.com/gitpython-developers/gitpython/milestone/32?closed=1

3.0.4

=============================================

see the following for details:
https://github.com/gitpython-developers/gitpython/milestone/31?closed=1

3.0.3

=============================================

see the following for (most) details:
https://github.com/gitpython-developers/gitpython/milestone/30?closed=1

3.0.2

=============================================

* fixes an issue with installation

3.0.1

=============================================

* Fix a `performance regression <https://github.com/gitpython-developers/GitPython/issues/906>`_ which could make certain workloads 50% slower
* Add `currently_rebasing_on` method on `Repo`, see `the PR <https://github.com/gitpython-developers/GitPython/pull/903/filesdiff-c276fc3c4df38382ec884e59657b869dR1065>`_
* Fix incorrect `requirements.txt` which could lead to broken installations, see this `issue <https://github.com/gitpython-developers/GitPython/issues/908>`_ for details.

3.0.0 - Remove Python 2 support
===============================

Motivation for this is a patch which improves unicode handling when dealing with filesystem paths.
Python 2 compatibility was introduced to deal with differences, and I thought it would be a good idea
to 'just' drop support right now, mere 5 months away from the official maintenance stop of python 2.7.

The underlying motivation clearly is my anger when thinking python and unicode, which was a hassle from the
start, at least in a codebase as old as GitPython, which totally doesn't handle encodings correctly in many cases.

Having migrated to using `Rust` exclusively for tooling, I still see that correct handling of encodings isn't entirely
trivial, but at least `Rust` makes clear what has to be done at compile time, allowing to write software that is pretty
much guaranteed to work once it compiles.

Again, my apologies if removing Python 2 support caused inconveniences, please see release 2.1.13 which returns it.

see the following for (most) details:
https://github.com/gitpython-developers/gitpython/milestone/27?closed=1

or run have a look at the difference between tags v2.1.12 and v3.0.0:
https://github.com/gitpython-developers/GitPython/compare/2.1.12...3.0.0.

2.1.13 - Bring back Python 2.7 support
======================================

My apologies for any inconvenience this may have caused. Following semver, backward incompatible changes
will be introduced in a minor version.

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/