Add Interface suffix

src/Extend/ExtenderInterface.php

@@ -0,0 +1,20 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Extend;
+
+use Flarum\Extension\Extension;
+use Illuminate\Contracts\Container\Container;
+
+interface ExtenderInterface
+{
+    public function __invoke(Container $container, Extension $extension = null);
+}