scale(x, y = x) {
		this.currentTransform.scale(x, y);
		this.updateBounds();
		this.isDirty = true;
		return this;
	}
scale the renderable around his anchor point.  Scaling actually applies changes
to the currentTransform member wich is used by the renderer to scale the object
when rendering.  It does not scale the object itself.  For example if the renderable
is an image, the image.width and image.height properties are unaltered but the currentTransform
member will be changed.
@param {number} x - a number representing the abscissa of the scaling vector.
@param {number} [y=x] - a number representing the ordinate of the scaling vector.
@returns {Renderable} Reference to this object for method chaining