title: Why does NelmioApiDocBundle generate the Nelmio doc, but cannot generate Swagger json?
body: <p>I started a fresh Symfony 2.8 project that I would like to document using swagger.
  I installed <a href="https://symfony.com/doc/master/bundles/NelmioApiDocBundle/index.html" rel="nofollow noreferrer">NelmioApiDocBundle</a> and it is working fine. Here is my only route:</p>
  
  <pre><code>/**
   *
   * @ApiDoc(
   *     section="Notification",
   *      resource=true,
   *   description="This method receive a notification and send it to the people concerned",
   *   parameters={
   *      {"name"="message", "dataType"="string", "required"=true, "description"="The message to be send"}
   *  })
   *
   * @Route("/notify")
   * @Method("POST")
   * @param Request $request
   *
   * @return JsonResponse
   */
  public function postNotifyAction(Request $request)
  { ...
  </code></pre>
  
  <p>My routing.yml:</p>
  
  <pre><code>notification:
      resource: "@NotificationBundle/Controller/"
      type:     annotation
      prefix:   /
  NelmioApiDocBundle:
      resource: "@NelmioApiDocBundle/Resources/config/routing.yml"
      prefix:   /api/doc
  nelmio_api_swagger:
      resource: "@NelmioApiDocBundle/Resources/config/swagger_routing.yml"
      prefix: /api/swagger
  </code></pre>
  
  <p>When I access the route <code>/api/doc</code> it is working fine:</p>
  
  <p><a href="https://i.stack.imgur.com/hP01N.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/hP01N.png" alt="Nelmio doc"></a></p>
  
  <p>But the swagger one: <code>/api/swagger</code> (that should be working according to: <a href="https://symfony.com/doc/current/bundles/NelmioApiDocBundle/swagger-support.html" rel="nofollow noreferrer">This doc</a>) is empty for my route:</p>
  
  <p><a href="https://i.stack.imgur.com/taWAS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/taWAS.png" alt="enter image description here"></a></p>
  
  <p>The command app/console <code>api:swagger:dump</code> is working fine:
  <a href="https://i.stack.imgur.com/XnRLY.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/XnRLY.png" alt="enter image description here"></a></p>
  
  <p>Am I missing something ?</p>