remove unknown shorthand flag for docker command.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

Makefile

@@ -61,7 +61,7 @@ ifeq ($(tag),)
 	@echo "Usage: make $@ tag=<tag>"
 	@exit 1
 endif
-	docker tag -f $(PRODUCTION_IMAGE):latest $(DEPLOY_ACCOUNT)/$(PRODUCTION_IMAGE):$(tag)
+	docker tag $(PRODUCTION_IMAGE):latest $(DEPLOY_ACCOUNT)/$(PRODUCTION_IMAGE):$(tag)
 	docker push $(DEPLOY_ACCOUNT)/$(PRODUCTION_IMAGE):$(tag)
 
 bundle: