ref(Makefile): remove obsolete "docker tag -f" flag

mboersma · mboersma · commit ca8244f1483e · 2016-06-20T15:24:14.000-06:00
This is an error with Docker 1.12.
diff --git a/Makefile b/Makefile
@@ -50,7 +50,7 @@ update-changelog:
 
 docker-build: build
 	docker build --rm -t ${IMAGE} rootfs
-	docker tag -f ${IMAGE} ${MUTABLE_IMAGE}
+	docker tag ${IMAGE} ${MUTABLE_IMAGE}
 
 # Push to a registry that Kubernetes can access.
 docker-push:
