Add Linux support

[toluschr]

Since me and perhaps some other people might want to use this script on Linux, I added support for it.

I also analyzed your script using shellcheck. It reported that exit codes should have a value from 0-255. I corrected this.

[toluschr]

I noticed that my editor used tabs instead of spaces, when I saved the document.
I corrected this and squashed the commits.

[eugr]

Thanks! For some reason I haven't got any notifications about this pull request. I'll check if it breaks anything on Mac and merge if everything is good.

[eugr]

@toluschr - any reason you got rid of sort in the pipeline? I used it to make sure we always update the latest Cura version.

[toluschr]

It worked without sort when I tested it, but I can add the sort back in if you want

[eugr]

Yeah, let's add it back is this 'find' behavior is not guaranteed on all platforms.

[toluschr]

I made the changes to the install script