correcting the url for model.js source file so the jsfiddle demo page works correctly.
Old url gave the following error: "Refused to execute script from 'https://raw.github.com/dgeorges/modeljs/v2.1.1/src/model.js' because its MIME type ('text/plain') is not executable, and strict MIME type checking is enabled. "
This new one should have the correct mime type.