Bootstrap selectpicker bug with bootstrap.js

HTML

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.6.5/css/bootstrap-select.min.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.6.5/js/bootstrap-select.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js"></script>
<select class="form-control deptId selectpicker" name="depId" placeholder="Department Name">
    <option selected="selected">Select department name</option>
    <option>Depart 1</option>
    <option>Depart 2</option>
    <option>Depart 3</option>
    <option>Depart 4</option>
    <option>Depart 5</option>
</select>

JavaScript

$('.selectpicker').selectpicker({
    style: 'btn-default',
    size: 4
});