title: Woocommerce default placeholder not gone in checkout form
body: <p>I'm using woocommerce_checkout_fields to change labels and fields.Below is my code</p>
  
  <pre><code>function custom_override_checkout_fields($fields) {
  
  
       $fields['billing']['billing_first_name'] = array(
              'label' =&gt; '',
              'placeholder' =&gt; _x('First Name*', 'placeholder', 'woocommerce'),
              'required' =&gt; true,
              'class' =&gt; array('checkout-billing-first-name')
          );
          $fields['billing']['billing_last_name'] = array(
              'label' =&gt; '',
              'placeholder' =&gt; _x('last Name*', 'placeholder', 'woocommerce'),
              'required' =&gt; true,
              'class' =&gt; array('checkout-billing-last-name')
          );
          $fields['billing']['billing_company'] = array(
              'label' =&gt; '',
              'placeholder' =&gt; _x('Company Name', 'placeholder', 'woocommerce'),
              'required' =&gt; false,
              'class' =&gt; array('checkout-billing-company')
          );
          $fields['billing']['billing_address_1'] = array(
              'label' =&gt; '',
              'placeholder' =&gt; _x('Address(Line 1)*', 'placeholder', 'woocommerce'),
              'required' =&gt; true,
              'class' =&gt; array('checkout-billing-addressL1')
          );
           $fields['billing']['billing_address_2'] = array(
              'label' =&gt; '',
              'placeholder' =&gt; _x('Address(Line 2)*', 'placeholder', 'woocommerce'),
              'required' =&gt; false,
              'class' =&gt; array('checkout-billing-addressL2')
          );
  
          return $fields;
      }
  
      add_filter('woocommerce_checkout_fields', 'custom_override_checkout_fields');
  </code></pre>
  
  <p>Everything works fine but placeholder for billing address 1 and billing address 2 is changing for only
  in loading i.e after page is loaded default placeholder are shown. </p>