title: WP_Query and acf date field does not sort right
body: <p>I am trying to only see posts after or equal to today and sort ASC, my date field outputs Ymd, the first part (only see posts after or equal to today) works but the sorting does not.</p>
  <pre><code>$today = date ('Ymd');
  $args = array(
      'post_type' =&gt; 'diensten', 
      'posts_per_page'    =&gt; -1,   
      'meta_query' =&gt; array(
          array(
              'key' =&gt; 'datum_dienst',
              'value' =&gt; $today,
              'compare' =&gt; '&gt;='
          )
      ),
      'meta_key'  =&gt; 'datum_dienst',
      'orderby'   =&gt; 'meta_value_num',
      'order'     =&gt; 'ASC',
  );
  $loop = new WP_Query( $args );
  </code></pre>