Support for the flatpak version

[hmlendea]

Hello,

It would be really nice if the script would auto-detect and use the flatpak version if it exists.

E.g. if /var/lib/flatpak/exports/bin/com.visualstudio.code exists, then use com.visualstudio.code (it's visible in the $PATH var), otherwise use code.

If you want I can try to make a pull request for this functionality myself. Just let me know if it's something you would accept as part of your project.

PS: This issue is kinda-but-not-quite similar to #15