message: docs(aio): fix promises link in toh-pt4
  closes
diff: @@ -420,7 +420,7 @@ The service does that work and eventually calls the function with the results or
  This is a simplified explanation. Read more about ES2015 Promises in the
  [Promises for asynchronous programming](http://exploringjs.com/es6/ch_promises.html) page of
  -[Exploring ES6](http://http://exploringjs.com/es6.html).
  +[Exploring ES6](http://exploringjs.com/es6.html).
  </div>
  