Scale the image
@param {number} scaleX - The scale ratio on the x-axis.
@param {number} [scaleY=scaleX] - The scale ratio on the y-axis.
@returns {Cropper} this
function scale(scaleX) {
    var scaleY = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : scaleX;
    var imageData = this.imageData;
    var transformed = false;
    scaleX = Number(scaleX);
    scaleY = Number(scaleY);

    if (this.ready && !this.disabled && this.options.scalable) {
      if (isNumber(scaleX)) {
        imageData.scaleX = scaleX;
        transformed = true;
      }

      if (isNumber(scaleY)) {
        imageData.scaleY = scaleY;
        transformed = true;
      }

      if (transformed) {
        this.renderCanvas(true, true);
      }
    }

    return this;
  }