Return a new can.compute every time (new can.view.Scope()).compute() is called

You need to actually return the new compute, so https://github.com/bitovi/canjs/blob/master/view/bindings/bindings.js#L62 won't get `undefined` back, resulting in an error here https://github.com/bitovi/canjs/blob/master/view/bindings/bindings.js#L187