title: kartik Select2 FilterType in gridview doesn't work
body: <p>I have an issue about kartik select2 filterType that doesn't work , this is a portion of my code :</p>
  
  <pre><code>[
                      'format' =&gt; ['link',$idmodel],
                      'attribute' =&gt;$attribute,
                      'filterType'=&gt;GridView::FILTER_SELECT2,
                      'filterWidgetOptions' =&gt; [
                      'data' =&gt; \yii\helpers\ArrayHelper::map($model_::find()-&gt;all(),$attribute,'nom_'.strtolower($idmodel)),
                      'options' =&gt; ['placeholder' =&gt; '-'.$idmodel.'-'],
                      'pluginOptions' =&gt; ['allowClear' =&gt; true],
                      'theme' =&gt; Select2::THEME_KRAJEE,
  
                      ],  
  </code></pre>
  
  <p>When i comment this line :</p>
  
  <pre><code>'filterType'=&gt;GridView::FILTER_SELECT2,
  </code></pre>
  
  <p>a text field appear in my filter grid view.
  Can any one help me ??
  Thanks in advance</p>