Update gcr.io/k8s-skaffold/pack image to v0.12.0
Update gcr.io/k8s-skaffold/pack image to v0.12.0

Fixes #4473

Signed-off-by: David Gageot <aa743a0aaec8f7d7a1f01442503957f4d7a2d634@gageot.net>
GoogleContainerTools/skaffold,GoogleContainerTools/skaffold,GoogleContainerTools/skaffold,GoogleContainerTools/skaffold,GoogleContainerTools/skaffold,GoogleContainerTools/skaffold,GoogleContainerTools/skaffold,GoogleContainerTools/skaffold,GoogleContainerTools/skaffold