The links in the demo are broken.
Could you replace them with the ones from cdn.jsdelivr.net?
<script src="https://cdn.jsdelivr.net/npm/diff_match_patch/lib/diff_match_patch.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/jquery-prettytextdiff/jquery.pretty-text-diff.min.js"></script>
The links in the demo are broken.
Could you replace them with the ones from cdn.jsdelivr.net?
https://jsfiddle.net/1xhqgy2L/