Fix "No module named 'gitdb.utils.compat'" error

[igortg]

This commit pins gitdb2 to 3.0.0 since it appears that version 3.0.2
has some braking changes.

(gitpython-test) λ $ py
Python 3.6.7 | packaged by conda-forge | (default, Nov  6 2019, 16:19:42) 
[GCC 7.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import git
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/igor/w/meta/envs/gitpython-test/lib/python3.6/site-packages/git/__init__.py", line 38, in <module>
    from git.exc import *                       # @NoMove @IgnorePep8
  File "/home/igor/w/meta/envs/gitpython-test/lib/python3.6/site-packages/git/exc.py", line 9, in <module>
    from git.compat import UnicodeMixin, safe_decode, string_types
  File "/home/igor/w/meta/envs/gitpython-test/lib/python3.6/site-packages/git/compat.py", line 16, in <module>
    from gitdb.utils.compat import (
ModuleNotFoundError: No module named 'gitdb.utils.compat'

Checklist

• Used a fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• Reset the build number to 0 (if the version changed)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[tadeu]

Awesome, thanks @igortg!

It looks like the breaking change has been the removal in this PR

[Harmon758]

See gitpython-developers/GitPython#983.