minus(duration) {
    if (!this.isValid) return this;
    const dur = Duration.fromDurationLike(duration).negate();
    return clone(this, adjustTime(this, dur));
  }
Subtract a period of time to this DateTime and return the resulting DateTime
See {@link DateTime#plus}
@param {Duration|Object|number} duration - The amount to subtract. Either a Luxon Duration, a number of milliseconds, the object argument to Duration.fromObject()
   @return {DateTime}