title: Symfony FOSRest return html instead json
body: <p>Hello I'm working on a migration symfony 2.7 -> symfony 3.4.
  My API routes have not worked since I migrated. When I test them they send me an answer in 200 htlm / text instead of JSON. I have verfier my entities, my controllers and I try another configuration of the bundle but I got no result.</p>
  
  <p>I work with jmserializer.</p>
  
  <p>Here is my Bundle configuration.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>fos_rest:
    param_fetcher_listener:
      enabled: true
    body_listener: true
    format_listener: true
    view:
      view_response_listener: 'force'
      formats:
        json : true
        xml: true
      templating_formats:
        html: true
      force_redirects:
        html: true
      failed_validation: HTTP_BAD_REQUEST
      default_engine: twig
    routing_loader:
      default_format: json
      prefix_methods: false</code></pre>
  </div>
  </div>
  </p>