title: Symfony 3.1 Yaml translation not working
body: <p>I am trying to set translations for my Symfony 3.1 Project. I have added the following line to my <code>app/config/config.yml</code>:</p>
  
  <pre><code>translator: { fallback: en }
  </code></pre>
  
  <p>I have added a messages.en.yaml file in <code>app/Resources/translations/</code> with just one string:</p>
  
  <pre><code>firstname: Test
  </code></pre>
  
  <p>Now i am trying to access it on my twig file like :</p>
  
  <pre><code>&lt;h1&gt;{% trans %} firstname {% endtrans %}&lt;/h1&gt;
  </code></pre>
  
  <p>I also tried to translate the string on DefaultController.php and the same error happens there as well:</p>
  
  <pre><code>use Symfony\Component\Translation\Translator;
  use Symfony\Component\Translation\Loader\YamlFileLoader;
  ....
  $translatedMessage = $this-&gt;get('translator')-&gt;trans('firstname');
  var_dump($translatedMessage);
  return $this-&gt;render('Default:index.html.twig');
  </code></pre>
  
  <p>When i try to access the page it gives me error like this:</p>
  
  <blockquote>
    <p>The "yaml" translation loader is not registered.</p>
  </blockquote>
  
  <p>I have tried installing all the following packages into my project as well like: </p>
  
  <pre><code>composer require symfony/yaml
  composer require symfony/translation
  </code></pre>
  
  <p>Please help. I am not sure what to try next.</p>