Added a Ruby sample which is wrongly detected as Perl

I’m not sure about the `.script!` extension, but I saw this everywhere in this repo. My [original file][ud] has no extension and is wrongly reported as Perl.

[ud]: https://github.com/bfontaine/ud/blob/9af56735c8b6c94e1ef092ac6f67397f4c73895f/bin/ud