Use `-n` instead of `! -z`, fix ShellCheck SC2236 in generate-stackbrew-pr.sh
Use `-n` instead of `! -z`, fix ShellCheck SC2236 in generate-stackbrew-pr.sh

chorrell/docker-node,pesho/docker-node,nodejs/docker-node,chorrell/docker-node,nodejs/docker-node,joyent/docker-node