title: Typescript thinks getYear does not exist on type Date
body: <p>I'm running tsc inside a webpack project, with <code>"core-js": "registry:dt/core-js#0.0.0+20160725163759"</code> and <code>"node": "registry:dt/node#6.0.0+20160909174046"</code></p>
  
  <p>Other date properties work fine:</p>
  
  <pre><code>private dateToString (date: Date) {
      let month = date.getMonth();
      let day = date.getDate();
      let year = date.getYear() + 1900;
  
      let dateString = `${month}/${day}/${year}`;
      return dateString;      
  }
  </code></pre>
  
  <p>Typescript recognizes <code>date.getMonth</code> and <code>date.getDate</code> just fine, but on <code>date.getYear</code> it gives</p>
  
  <p><code>Property 'getYear' does not exist on type 'Date'.</code></p>
  
  <p>What definition am I missing?</p>