title: LiipImagineBundle not working on production environment
body: <p>I use <code>LiipImagineBundle 1.6.0</code> on <code>Symfony 3.1.3</code> combined with <code>VichUploaderBundle 1.2.0</code> and everything goes fine on <code>dev</code> but on <code>prod</code> he doesn't save cached files. Images are saving correctly so there is rather not a problem of <code>VichUploaderBundle</code>.</p>
  
  <p>config.yml:</p>
  
  <pre><code>vich_uploader:
      db_driver: orm # or mongodb or propel or phpcr
      mappings:
              pop_image:
                  uri_prefix:         /images/pops
                  upload_destination: %kernel.root_dir%/../web/images/pops
              ad_image:
                  uri_prefix:         /images/ads
                  upload_destination: %kernel.root_dir%/../web/images/ads
  liip_imagine:
      resolvers:
         default:
            web_path: ~
  
      filter_sets:
          cache: ~
          square:
              quality: 75
              filters:
                  thumbnail: { size: [400, 400], mode: outbound }
  </code></pre>
  
  <p>routing.yml:</p>
  
  <pre><code>_liip_imagine:
      resource: "@LiipImagineBundle/Resources/config/routing.xml"
  </code></pre>
  
  <p>twig:</p>
  
  <pre><code>...
  &lt;div class="image"&gt;
     &lt;img src="{{ vich_uploader_asset(pop,'imageFile')|imagine_filter('square') }}" alt="{{ pop.question }}" width="100%" class="grayscale" /&gt;
     &lt;span class="image-question"&gt;{{ pop.question }}&lt;/span&gt;
  &lt;/div&gt;
  ...
  </code></pre>