title: mongoose findOne with sorting
body: <p>I have a problem with a mongo request:</p>
  <pre><code>models.user.findOne(
      {},
      {
          sort: {
              date_register: -1
          }
      },
      function(err, result) {
          console.log(err);
  }
  </code></pre>
  <p>I have</p>
  <pre><code>{ [MongoError: Error: Unsupported projection option: date_register] name: 'MongoError' }
  </code></pre>
  <p>as error</p>
  <p>I'd like to get my users by date_register DESC</p>
  <p>Thanks</p>