title: dispatcher doesn't dispatch my event symfony
body: <p>I have an ExampleListener class that look like : </p>
  
  <pre><code>&lt;?php
  
  namespace AppBundle\EventListener;
  
  class ExampleListener
  {
      public function helloWorld()
      {
          echo "Hello World!";
      }
  }
  </code></pre>
  
  <p>This is my services.yml</p>
  
  <pre><code>services:
      my.event:
          class: AppBundle\EventListener\ExampleListener
          tags:
              - { name: kernel.event_listener, event: my.event, method: helloWorld }
  </code></pre>
  
  <p>And then from controller i'm trying to dispatch the event.</p>
  
  <pre><code>$dispatcher = new EventDispatcher();
  $dispatcher-&gt;dispatch('my.event')
  </code></pre>
  
  <p>I don't have any error but the helloWorld function is never called.
  My event is up :</p>
  
  <blockquote>
    <p>php bin/console debug:event-dispatcher my.event</p>
  </blockquote>
  
  <p>the result is :</p>
  
  <pre><code>#1      AppBundle\EventListener\ExampleListener::helloWorld()   0
  </code></pre>
  
  <p>Why dispatcher doens't call the event right?
  Thanks.</p>