function isSpecial(scheme) {
  return (
    scheme === 'file:' ||
    scheme === 'ftp:' ||
    scheme === 'http:' ||
    scheme === 'https:' ||
    scheme === 'ws:' ||
    scheme === 'wss:'
  );
}
Check whether a protocol scheme is special.

@param {String} The protocol scheme of the URL
@return {Boolean} `true` if the protocol scheme is special, else `false`
@private