title: Why does the function `dump` not exist in twig file?
body: <p>I don't know why it shows this error</p>
  
  <pre><code>The function "dump" does not exist in twig file
  </code></pre>
  
  <p>while I have already writen in <code>config.yml</code> file:</p>
  
  <pre><code>services:
  product_store.twig.extension.debug:
      class: Twig_Extension_Debug
      tags:
           - { name: 'twig.extension' }
  </code></pre>
  
  <p>and in twig file I try to dump  with:</p>
  
  <pre><code>{{ dump(product) }}
  </code></pre>