title: Strange indexable styping
body: <p>Typescript (2.0) doesn't give an error on this:</p>
  
  <pre><code>let x: { [index: string]: Object } = {1: 2}
  </code></pre>
  
  <p>I see there two potential errors: </p>
  
  <ol>
  <li>Index field is number type but should be string</li>
  <li>item type is number too but should be an Object type</li>
  </ol>
  
  <p>Why does it passes?</p>