title: Yii2 Select2 also spans original select
body: <p>I'm trying to use <code>Select2</code> widget in Yii2 but it's rendering both the Select2 dropdown and the original dropdown. </p>
  
  <pre><code> &lt;div class="homepage-searchbar"&gt;
      &lt;div class="container"&gt;
          &lt;div class="row"&gt;
              &lt;div class="col-md-12"&gt;
                  &lt;div class="align-middle"&gt;
                      &lt;div class="col-md-3 col-sm-3"&gt;
                          &lt;?php
                          $dataCategory=ArrayHelper::map(City::find()-&gt;all(),'id', 'city_name');
  
                          echo $form-&gt;field($searchModel, 'city_id')-&gt;widget(Select2::classname(), [
                              'data' =&gt; $dataCategory,
                              'theme' =&gt; Select2::THEME_BOOTSTRAP,
                              'options' =&gt; ['placeholder' =&gt; 'Select a city ...'],
                              'pluginOptions' =&gt; [
                                  'allowClear' =&gt; true,
                              ],
                          ])-&gt;label(false); ?&gt;
                      &lt;/div&gt;
                      &lt;div class="col-md-3 col-sm-3"&gt; 
                          &lt;?php echo \yii\helpers\Html::submitButton(Yii::t('frontend','Search Now'), ['class' =&gt; 'btn btn-default','onclick'=&gt;'return searchRooms()']) ?&gt;
                      &lt;/div&gt;
                  &lt;/div&gt;
              &lt;/div&gt;
          &lt;/div&gt;    
      &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>This is what it looks like:</p>
  
  <p><a href="https://i.stack.imgur.com/IaUk0.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IaUk0.png" alt="screen"></a></p>