Actually run the clean-docker command instead of echoing it

Makefile

@@ -54,7 +54,7 @@ release:
 clean-docker:
 	$(eval containers:=$(shell docker ps -a -q))
 	@if [ -n "$(containers)" ]; then \
-		echo "Cleaning up past containers\n" \
+		echo "Cleaning up past containers\n" ; \
 		docker rm -f $(containers) ; \
 	fi