title: Class 'Symfony\Component\EventDispatcher\Event' not found in Laravel/Lumen
body: <p>When Trying to install Rackspace package (<code>composer require rackspace/php-opencloud</code>), getting the following error
  <code>Class 'Symfony\Component\EventDispatcher\Event' not found</code>.
  I have installed symfony package but that could not worked out.
  Kindly help me out for this.</p>