LE, like OpenElec is a read only system, so the script will fail as it cannot write to the system files. Looking at the script it is definitely designed
to work on most "Normal" Raspbian systems, including OSMC and probably Xbian (With a few modifications) but not LE.
However, someone may have managed to get it working on LE.
Their installation script installs various software via apt-get, which is a debian (and debian based) thing, and via pip (a python installer).
To properly install on LibreELEC you'd need to look at the installer and work out what other software is needed on Libreelec and then creating packages for the dependencies, all quite complex.
Or docker may assist...
you actually need the scripts from here GitHub - pimoroni/clean-shutdown: Python daemon to watch a GPIO pin and trigger a clean shutdown.
It looks like it should all work, but you need to edit a lot of path's and make a systemd unit file to get it to work.
My option: just leave the Pi on all the time 
