title: Option footer-html returning error when used within KnpSnappyBundle
body: <p>I'm trying to build invoice pdf with wkhtmltopdf library and a symfony2 wrapper <a href="https://github.com/KnpLabs/snappy" rel="nofollow">KnpSnappyBundle</a>.</p>
  
  <p>I want to add a footer on every page with the wkhtmltopdf option footer-html. In command-line, everything works fine, my pdf is built and a footer is repeated on every page. But when I use the bundle service : </p>
  
  <pre><code>$snappy = $this-&gt;get('knp_snappy.pdf');
  $snappy-&gt;setOption('footer-html', 'http://www.google.com');
  $content = $snappy-&gt;getOutputFromHtml($html);
  
  return new Response(
      $content,
      200,
      array(
          'Content-Type'          =&gt; 'application/pdf',
          'Content-Disposition'   =&gt; 'attachment; filename="file.pdf"'
      )
  );
  </code></pre>
  
  <p>it returns an error :</p>
  
  <pre><code>The exit status code '1' says something went wrong:
  stderr: "Loading pages (1/6)
  [&gt; ] 0%
  [======&gt; ] 10%
  Error: Failed loading page http://www.google.com (sometimes it will work just to ignore this error with --load-error-handling ignore)
  Exit with code 1 due to network error: HostNotFoundError
  "
  stdout: ""
  command: C:\wkhtmltopdf\bin\wkhtmltopdf.exe --lowquality --dpi "300" --margin-bottom "0" --margin-left "0" --margin-right "0" --margin-top "0" --page-size "A4" --background --encoding "utf-8" --footer-html "http://www.google.com" "http://www.google.com" "test.pdf".
  </code></pre>
  
  <p>Did any already succeed in using footer-html option with KnpSnappyBundle ?</p>