title: yii2 ActiveForm field placeholder
body: <p>I want to create form using yii2 ActiveForm. Here is my code:</p>
  
  <pre><code>&lt;?php
  $form = \yii\widgets\ActiveForm::begin([
      'options' =&gt; [
          'class' =&gt; 'form-inline'
          ]
  ]);
  ?&gt;
  &lt;div class="form-group"&gt;
       &lt;label class="sr-only" for="example"&gt;Email&lt;/label&gt;
       &lt;?php echo $form-&gt;field($model, 'email', [
             'inputOptions' =&gt; ['autofocus' =&gt; 'autofocus', 'class' =&gt; 'form-control transparent']
       ])-&gt;textInput(['placeholder' =&gt; "Enter Your Email"])-&gt;input('email')-&gt;label(false); ?&gt;
  &lt;/div&gt;
  
  
  &lt;button type="submit" class="subscr-btn btn btn-primary btn-fill"&gt;Join&lt;/button&gt;
  &lt;?php \yii\widgets\ActiveForm::end(); ?&gt;
  </code></pre>
  
  <p>which generates this html:</p>
  
  <pre><code>&lt;form id="w0" class="form-inline" action="/example" method="post"&gt;
  &lt;div class="form-group"&gt;
      &lt;label class="sr-only" for="exampleInputEmail2"&gt;Email address&lt;/label&gt;
      &lt;div class="form-group field-subscriber-email required"&gt;
          &lt;input type="email" id="subscriber-email" class="form-control transparent" name="Subscriber[email]"
                 autofocus="autofocus"&gt;
          &lt;div class="help-block"&gt;&lt;/div&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  &lt;button type="submit" class="subscr-btn btn btn-primary btn-fill"&gt;Join&lt;/button&gt;
  </code></pre>
  
  <p></p>
  
  <p>Everything is ok, but where is placeholder?</p>