title: how to set placeholder default display in bootstrap-daterangepicker
body: <p>HTML:</p>
  
  <pre><code>&lt;input type="text" name="form" placeholder="Check In"&gt;
  </code></pre>
  
  <p>JS:</p>
  
  <pre><code>$('input[name="form"]').daterangepicker({
      singleDatePicker: true,
      showDropdowns: true,
  });
  </code></pre>
  
  <p>I want to look like this.</p>
  
  <p><a href="http://i.stack.imgur.com/lx9SE.png" rel="noreferrer">example</a></p>
  
  <p>bootstrap-daterangepicker official website：<a href="http://www.daterangepicker.com/" rel="noreferrer">http://www.daterangepicker.com/</a></p>