title: Yii2 doesn't redirect to index page after update action
body: <p>My Update buttons code:</p>
  
  <pre><code>&lt;div class="form-group"&gt;
      &lt;?= Html::submitButton($model-&gt;isNewRecord ? 'Create' : 'Update', ['class' =&gt; $model-&gt;isNewRecord ? 'btn btn-success' : 'btn btn-primary']) ?&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>and in updateAction I have:</p>
  
  <pre><code>if ($model-&gt;load(Yii::$app-&gt;request-&gt;post()) &amp;&amp; $model-&gt;save()) {
      return $this-&gt;redirect(['index']);
  } else {
      return $this-&gt;render('update']);
  }
  </code></pre>
  
  <p>but when I update my form and press Update button it updates values BUT it return me the UPDATE page, doesn't redirect to index. What is the problem?</p>