Sample manifests uses deprecated APIs.

[musaprg]

I noticed that manifests in kubernetes/ didn't work. I got the error below.

$ kubectl apply -f kubernetes/helloworld-deployment.yaml
error: unable to recognize "kubernetes/helloworld-deployment.yaml": no matches for kind "Deployment" in version "extensions/v1beta1"

From Kubernetes v1.16 release, "Deployment" in extensions/v1beta1 has migrated to apps/v1.
To walk-through this workshop on the cluster whose version is v1.16 above, we need to modify apiVersion of manifests to apps/v1.
reference: https://kubernetes.io/blog/2019/07/18/api-deprecations-in-1-16/

It might be helpful to note this deprecation in the tutorial or fix sources.