Use of environment vars in paths is deprecated, Warning in Python 3.7

```
warnings.warn("The use of environment variables in paths is deprecated" +
/usr/local/lib/python3.7/dist-packages/git/repo/base.py:127: UserWarning: The use of environment variables in paths is deprecated for security reasons and may be removed in the future!!
```

However, I'm passing absolute paths to the Repo class, this creates a lot of warning messages in the script output