title: Format option in vue-datetime wrong format
body: <p>I'm using <code>vue-datetime</code> plugin, it appears as if the <code>format</code> option doesn't work as expected, see below:</p>
  
  <pre><code>&lt;datetime type="date" v-model="formData.testDate" input-class="form-control" format="DateTime.DATE_SHORT"&gt;&lt;/datetime&gt;
  </code></pre>
  
  <p>It should output as: <code>DD/MM/YYYY</code> but instead outputs as a random string of characters.</p>
  
  <p><a href="https://i.stack.imgur.com/Ctwil.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Ctwil.png" alt="enter image description here"></a></p>