title: Timeout issue generate wkhtmltopdf in symfony 2.4 knpSnappy bundle
body: <p>When i download pdf using knpSnappy bundle , sometimes it's working proper and sometimes it's not working. </p>
  
  <p>It generates errors like this:</p>
  
  <blockquote>
    <p>The process "/usr/local/bin/wkhtmltopdf --margin-bottom '0'
    --margin-left '0' --margin-right '0' --margin-top '0' --page-size 'A4' --disable-javascript --load-error-handling 'ignore' '/tmp/knp_snappy59521f8e31bad9.75401982.html'
    '/tmp/knp_snappy59521f8e31c3d6.47962749.pdf'" exceeded the timeout of
    60 seconds.</p>
  </blockquote>
  
  <p>Please help me to resolve this issue.</p>
  
  <p>Thanks</p>