InOut = function (v, overshoot)
{
    if (overshoot === undefined) { overshoot = 1.70158; }

    var s = overshoot * 1.525;

    if ((v *= 2) < 1)
    {
        return 0.5 * (v * v * ((s + 1) * v - s));
    }
    else
    {
        return 0.5 * ((v -= 2) * v * ((s + 1) * v + s) + 2);
    }
}
Back ease-in/out.

@function Phaser.Math.Easing.Back.InOut
@since 3.0.0

@param {number} v - The value to be tweened.
@param {number} [overshoot=1.70158] - The overshoot amount.

@return {number} The tweened value.