Doesn't display label on <optgroup></optgroup>

[rougin]

I try to display a dropdown using your library but it does not display the labels in the <optgroup>:

<select name="major_description" class="form-control">
    <optgroup label="Hello">
        <option value="world">foo</option>
    </optgroup>
    <optgroup label="World">
        <option value="bar">foot</option>
    </optgroup>
</select>

The result is it only displays the values foo and foot.

[f22hd]

me to , we need help