title: NodeJS is not serializing the ES6 Map
body: <p>This is my sample <code>javascript</code> code is being executed in <code>node.js</code></p>
  
  <pre><code>let commutertrip = new Map();
  let t = {
      userId: 1,
      capacity: 4,
      commuteId: 1,
      endTime: new Date(),
      id: 1,
      status: "QUEUED",
      startTime: new Date(),
      price: 100
  };
  commutertrip.set(1, t);
  let trip = {
      id: 2,
      poolerId: 3,
      poolerTrip: {
          capacity: 4,
          commuteId: 8,
          id: 1,
          endTime: new Date(),
          startTime: new Date(),
          status: "QUEUED",
          price: 55,
          userId: 1
      },
      commuterTrip: commutertrip,
      status: "QUEUED"
  };
  console.log(JSON.stringify(trip));
  </code></pre>
  
  <p>The output</p>
  
  <pre><code>{"id":2,"poolerId":3,"poolerTrip":{"capacity":4,"commuteId":8,"id":1,"endTime":"2016-07-27T06:59:51.773Z","startTime":"2016-07-27T06:59:51.773Z","status":"QUEUED","price":55,"userId":1},"commuterTrip":{},"status":"QUEUED"}
  </code></pre>
  
  <p>I didn't find how to fix this? The same <code>javascript</code> code works fine <a href="http://www.es6fiddle.net/ir4jnxzm/" rel="nofollow">here</a>
  Here's the node arguments <code>node --debug-brk=33172 --nolazy --harmony bin\www</code></p>