isort: format codebase

Change-Id: I6f11d123b68fd077f558d3c21349c55c5f251019
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/383715
Reviewed-by: Gavin Mak <gavinmak@google.com>
Tested-by: Mike Frysinger <vapier@google.com>
Commit-Queue: Mike Frysinger <vapier@google.com>

tests/test_git_command.py

@@ -14,11 +14,12 @@
 
 """Unittests for the git_command.py module."""
 
-import re
 import os
+import re
 import subprocess
 import unittest
 
+
 try:
     from unittest import mock
 except ImportError: