update() {

		const vmin = Math.min( window.innerWidth, window.innerHeight );
		const scale = Math.max( vmin / 5, 150 ) / vmin;
		const indices = this.Reveal.getIndices();

		this.Reveal.transformSlides( {
			overview: [
				'scale('+ scale +')',
				'translateX('+ ( -indices.h * this.overviewSlideWidth ) +'px)',
				'translateY('+ ( -indices.v * this.overviewSlideHeight ) +'px)'
			].join( ' ' )
		} );

	}
Moves the overview viewport to the current slides.
Called each time the current slide changes.