Oh damn sorry about that. Ok I think I've fixed it: https://github.com/dostee-hemin/Music-Rewind
It's the same link but I made it public. Please let me know if it works.
Ok that means that you need to install java 8.
Here is the link to their website: https://www.java.com/en/download/mac_download.jsp
If you don't feel comfortable doing this, that's totally fine it's up to you. Sorry for making you go through all this.