The SSL certificate on the Kendo CDN service(kendo.cdn.telerik.com) has expired. We are currently working on that. Any further information on the development will be posted in this thread.
Temporary you can use this https://da7xgjtj801h2.cloudfront.net/ instead of https://kendo.cdn.telerik.com e.g:
** The issue is now fixed. Please, accept our apology for the inconvenience caused!
*** A status page, where you can subscribe for notifications in case of future incidents is now available.