Kanboard requires at least PHP 5.6 now

vendor/symfony/event-dispatcher/ImmutableEventDispatcher.php

@@ -18,18 +18,8 @@ namespace Symfony\Component\EventDispatcher;
  */
 class ImmutableEventDispatcher implements EventDispatcherInterface
 {
-    /**
-     * The proxied dispatcher.
-     *
-     * @var EventDispatcherInterface
-     */
     private $dispatcher;
 
-    /**
-     * Creates an unmodifiable proxy for an event dispatcher.
-     *
-     * @param EventDispatcherInterface $dispatcher The proxied event dispatcher.
-     */
     public function __construct(EventDispatcherInterface $dispatcher)
     {
         $this->dispatcher = $dispatcher;
@@ -83,6 +73,14 @@ class ImmutableEventDispatcher implements EventDispatcherInterface
         return $this->dispatcher->getListeners($eventName);
     }
 
+    /**
+     * {@inheritdoc}
+     */
+    public function getListenerPriority($eventName, $listener)
+    {
+        return $this->dispatcher->getListenerPriority($eventName, $listener);
+    }
+
     /**
      * {@inheritdoc}
      */