gitrevision errors

[simon-mo]

modin/modin/__init__.py

Line 21 in cccea0b

git_revision = _execute_cmd_in_temp_env(['git', 'rev-parse', 'HEAD'])

Current git revision tries to find the git commit by executing Popen directly from user process. This will start wherever user process start, which might not be a git repository. To fix it, we just need to run above line inside modin.__file__ or something like that.