Clean page logs errors in console: `sinon is not defined`

Just going to requirebin.com and viewing the console shows `Uncaught ReferenceError: sinon is not defined`. 

I am not sure how long it has been like that, or if it is a new issue. If this is a new issue with Sinon I might be able to help, but we already supply a browserified build through NPM, so not totally sure how this manages to crash.