code: function statusCodes(allowed, ignored, options) {
    var stream = new Transform({objectMode: true});
    var errored = false;
  
    stream._transform = function (page, _, callback) {
      if (errored) return callback(null);
      if (ignored && ignored.indexOf(page.statusCode) !== -1) return callback(null);
      if (!allowed || allowed.indexOf(page.statusCode) !== -1) {
        stream.push(page);
        return callback(null);
      }
      errored = true;
      stream.emit('error', new Error('Invalid status code ' + page.statusCode + ' - ' + page.url));
      callback(null);
    };
  
    return stream;
  }
docs: Limit status codes to a list of allowed status codes
  
  @param {Array.<Number>} allowed
  @param {Array.<Number>} ignored
  @returns {TransformStream}