Using a CDN is only a problem if it's compromised, which is unlikely to be a threat for most applications. You can avoid this entirely by using Subresource Integrity:
https://developer.mozilla.org/en-US/docs/Web/Security/Subres...
It looks like the developer for this page copied the CDNJS links at some point but didn't do so consistently and later commented out the SRI portion of the jQuery tag:
<!--integrity="sha256-hwg4gsxgFZhOsEEamdOYGBf13FyQuiTwlAQgxVSNgt4="-->