code: function _updateFormatOut (formatOut, options) {
    if (!(is.object(options) && options.force === false)) {
      this.options.formatOut = formatOut;
    }
    return this;
  }
docs: Update the output format unless options.force is false,
  in which case revert to input format.
  @private
  @param {String} formatOut
  @param {Object} [options]
  @param {Boolean} [options.force=true] - force output format, otherwise attempt to use input format
  @returns {Sharp}