Make should only build the image, not publish.

(In gocd this is handled through an artifact.)

fpm/Makefile

@@ -3,4 +3,6 @@ SHELL:=/bin/bash
 ubuntu1804fpm:
 	docker pull rayburgemeestre/fpm-ubuntu:18.04 || true
 	docker build . -f Dockerfile -t rayburgemeestre/fpm-ubuntu:18.04
+
+publish:
 	docker push rayburgemeestre/fpm-ubuntu:18.04