Update requirements.txt

Hi there,

We are encountering the following error:

Command: python tableauBackup.py -p a

Error: Traceback (most recent call last): File "tableauBackup.py", line 5, in from git import Repo File "Python\lib\site-packages\git__init__.py", line 38, in from git.exc import * # @nomove @IgnorePep8 File "Python\lib\site-packages\git\exc.py", line 9, in from git.compat import UnicodeMixin, safe_decode, string_types File "Python\lib\site-packages\git\compat.py", line 16, in from gitdb.utils.compat import ( ModuleNotFoundError: No module named 'gitdb.utils.compat'

Resolution: add "gitdb2==3.0.1" to "requirements.txt"