title: yii2 DatePicker widget error
body: <p>Hello everyone I'm doing a form with dates , use the widget Kartik , but says </p>
  
  <blockquote>
    <p>Class ' kartik \ widgets \ DatePicker ' not found</p>
  </blockquote>
  
  <p>Any suggestions? Thank you</p>
  
  <p><strong>my code</strong></p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>use kartik\widgets\DatePicker;
  
   &lt;?php $form = ActiveForm::begin([
                      'id' =&gt; 'viaggio',
                      /*'enableAjaxValidation'   =&gt; true,
                      'enableClientValidation' =&gt; false,*/
                                   ]); ?&gt;
  &lt;?= $form-&gt;field($model, 'data_part')-&gt;widget(DatePicker::classname(), [
      'options' =&gt; ['placeholder' =&gt; 'Enter  ...'],
      'pluginOptions' =&gt; [
          'autoclose'=&gt;true
      ]
  ]); ?&gt;</code></pre>
  </div>
  </div>
  </p>