You should post these type of question in the issues over on the github repo, this is really not an ACF issue.
However, the ACF JS API was completely rewritten for ACF 5.7.0 and you will need to rewrite the JS used by the code you copied. I have done this for another of those examples and you can see the types of changes that need to be made there https://github.com/Hube2/acf-dynamic-ajax-select-example/blob/master/dynamic-select-example/dynamic-select-on-select.js
