functions.php

<?php
add_action( 'upgrader_process_complete', 'sentree_upgrader_process_complete', 10, 0 );
function sentree_upgrader_process_complete()
{
  error_log('Upgrade process complete');
  global $nginx_purger;

  if(isset($nginx_purger))
  {
    $nginx_purger->purge_all();
    error_log('Purging nginx cache after upgrade');
  }
}