Maybe reverse the if to see if it is ubuntu based else add latest LTS repo

Line 15 in 6e335a0

    
           if [ "$DIST_CODENAME" = "jessie" ] || [ "$DIST_CODENAME" = "stretch" ] || [ "$DIST_CODENAME" = "buster" ] || [ "$DIST_CODENAME" = "sid" ];

Some distros may change the codename of upstream (linux Mint), so it is better to check if it is an official spin or debian, else just add the LTS repo

Tested Linux Mint 18.2 Sonya. Works as expected. Closing it for the time being but will keep an eye if any other Ubuntu/Debian needs this to be opened again