[doc] Add JSDoc for the finishRequest option

Author: lpinca

lib/websocket.js

@@ -618,6 +618,8 @@ module.exports = WebSocket;
  * @param {(String|URL)} address The URL to which to connect
  * @param {Array} protocols The subprotocols
  * @param {Object} [options] Connection options
+ * @param {Function} [options.finishRequest] A function which can be used to
+ *     customize the headers of each http request before it is sent
  * @param {Boolean} [options.followRedirects=false] Whether or not to follow
  *     redirects
  * @param {Function} [options.generateMask] The function used to generate the