title: jquery.dropdown.js required not working
body: <p>I'm using the <code>jquery.dropdown.js</code> plugin. 
  My problem is there is no notification appear when submitting the form, leaving the required select tag with no value.</p>
  
  <p>html:</p>
  
  <pre><code>&lt;div class="dropdown-sin-1" style="margin-top: -15px;"&gt;
          &lt;select name="" placeholder="" required&gt;      
              &lt;option value="" disabled selected&gt;&lt;/option&gt;
              &lt;option value="1"&gt;1&lt;/option&gt;
              &lt;option value="2"&gt;2&lt;/option&gt;
              &lt;option value="3"&gt;3&lt;/option&gt;
              &lt;option value="4"&gt;4&lt;/option&gt;
              &lt;option value="5"&gt;5&lt;/option&gt;
              &lt;option value="6"&gt;6&lt;/option&gt;
              &lt;option value="7"&gt;7&lt;/option&gt;
          &lt;/select&gt;
          &lt;/div&gt;
  </code></pre>
  
  <p>js:</p>
  
  <pre><code>$('.dropdown-sin-1').dropdown({
    readOnly: false,
    limitCount: Infinity,
    input: '&lt;input type="text" maxLength="20" placeholder="Search"&gt;',
    data: [],
    searchable: true,
    searchNoData: '&lt;li style="color:#ddd"&gt;No Results&lt;/li&gt;',
    choice: function () {}
  });
  </code></pre>
  
  <p>fiddle: <a href="https://jsfiddle.net/tbge7f2m/" rel="nofollow noreferrer">https://jsfiddle.net/tbge7f2m/</a></p>