title: Delete intermediary files after elixir merge
body: <p>I am using Laravel 5. During gulp task, the processed SASS files and other CSS files copied from resource folder are stored in public/css. 
  Then all the files in the public/css are merged together to a single file as "all.css". So the files that were created needs to be deleted. </p>
  
  <p>How can I do this? </p>