fix markdown typo

Author: zeke

README.md

@@ -30,4 +30,4 @@ For more information about using Node.js on Heroku, see these Dev Center article
 - [Getting Started with Node.js on Heroku](https://devcenter.heroku.com/articles/nodejs)
 - [Heroku Node.js Support](https://devcenter.heroku.com/articles/nodejs-support)
 - [Building a Real-time, Polyglot Application with Node.js, Ruby, MongoDB and Socket.IO](https://devcenter.heroku.com/articles/realtime-polyglot-app-node-ruby-mongodb-socketio)
-- [Using Socket.IO with Node.js on Heroku]https://devcenter.heroku.com/articles/using-socket-io-with-node-js-on-heroku
+- [Using Socket.IO with Node.js on Heroku](https://devcenter.heroku.com/articles/using-socket-io-with-node-js-on-heroku)