The reply from CircleCI team was:
In order to reduce our burden on GitHub, we do a shallow clone instead of a full one. If this is a problem, you can try running git fetch --unshallow prior to running git rev-list --count HEAD.
The reply from CircleCI team was:
In order to reduce our burden on GitHub, we do a shallow clone instead of a full one. If this is a problem, you can try running git fetch --unshallow prior to running git rev-list --count HEAD.