https://jsfiddle.net/1yxnecgo/
The problem was passing a method to requestAnimationFrame. You have to instead wrap the method call in a function. To avoid losing the this context, I used an arrow function. Not that obvious, eh? 
PS: If you configure the renderer with antialias: true at construction, you will get smoother edges on the cube: https://jsfiddle.net/1yxnecgo/1/