Fix EventDispatcer & events

Looks like parameter for the `->dispatch(` have been flipped (event first then event name).
Define events should now extends `Symfony\Contracts\EventDispatcher\Event`

src/Wallabag/CoreBundle/Event/EntrySavedEvent.php

@@ -2,7 +2,7 @@
 
 namespace Wallabag\CoreBundle\Event;
 
-use Symfony\Component\EventDispatcher\Event;
+use Symfony\Contracts\EventDispatcher\Event;
 use Wallabag\CoreBundle\Entity\Entry;
 
 /**
@@ -19,7 +19,7 @@ class EntrySavedEvent extends Event
         $this->entry = $entry;
     }
 
-    public function getEntry()
+    public function getEntry(): Entry
     {
         return $this->entry;
     }