fix debian sysv init script
Hi!
I figured out that on Debian with sysvinit /etc/init.d/gitlab-runner status
command does not work. It reported that it must be run as root (while there's no real need for this), and even when being run as root it reported a error. I fixed this issue and also changed shebang to #!/bin/sh
because Debian does not rely on bash in its native init scripts.