Move scm.py to lib/

It belongs there.

Change-Id: I286b50c43c587c39557fc508175efbd4b0f51d51
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4289680
Reviewed-by: Joanna Wang <jojwang@chromium.org>
Commit-Queue: Josip Sokcevic <sokcevic@chromium.org>
diff --git a/git_migrate_default_branch.py b/git_migrate_default_branch.py
index 4e00d3d..fec10fb 100644
--- a/git_migrate_default_branch.py
+++ b/git_migrate_default_branch.py
@@ -8,7 +8,7 @@
 import gerrit_util
 import git_common
 import metrics
-import scm
+from lib import scm
 import sys
 import logging
 from six.moves import urllib