chore: bump pack version used in skaffold pack image
set -e
-PACK_VERSION=v0.21.1
+PACK_VERSION=v0.28.0
docker build . --build-arg PACK_VERSION=${PACK_VERSION} -t gcr.io/k8s-skaffold/pack:${PACK_VERSION} -t gcr.io/k8s-skaffold/pack:latest
docker push gcr.io/k8s-skaffold/pack:${PACK_VERSION}
