static back(s: number): (t: number) => number {
    if (s === undefined) {
      s = 1.70158;
    }
    return (t) => t * t * ((s + 1) * t - s);
  }
Use with `Animated.parallel()` to create a simple effect where the object
animates back slightly as the animation starts.

Wolfram Plot:

- http://tiny.cc/back_default (s = 1.70158, default)