Change the aspect ratio of the crop box.
@param {number} aspectRatio - The new aspect ratio.
@returns {Cropper} this
function setAspectRatio(aspectRatio) {
    var options = this.options;

    if (!this.disabled && !isUndefined(aspectRatio)) {
      // 0 -> NaN
      options.aspectRatio = Math.max(0, aspectRatio) || NaN;

      if (this.ready) {
        this.initCropBox();

        if (this.cropped) {
          this.renderCropBox();
        }
      }
    }

    return this;
  }