Update Makefile to replace deprecated gcloud docker

More modernization to get this running again.

Author: justinsb

guestbook-go/Makefile

@@ -23,11 +23,11 @@ release: clean build push clean
 
 # builds a docker image that builds the app and packages it into a minimal docker image
 build:
-	docker build -t ${REGISTRY}/guestbook:${VERSION} .
+	docker buildx build --load -t ${REGISTRY}/guestbook:${VERSION} .
 
 # push the image to an registry
 push:
-	gcloud docker -- push ${REGISTRY}/guestbook:${VERSION}
+	docker buildx build --push -t ${REGISTRY}/guestbook:${VERSION} .
 
 # remove previous images and containers
 clean: