Add back alias for moved class

system/src/Grav/Common/Twig/TwigExtension.php

@@ -0,0 +1,21 @@
+<?php
+
+/**
+ * @package    Grav\Common\Twig
+ *
+ * @copyright  Copyright (c) 2015 - 2021 Trilby Media, LLC. All rights reserved.
+ * @license    MIT License; see LICENSE file for details.
+ */
+
+namespace Grav\Common\Twig;
+
+use Grav\Common\Twig\Extension\GravExtension;
+
+/**
+ * Class TwigExtension
+ * @package Grav\Common\Twig
+ * @deprecated 1.7 Use GravExtension instead
+ */
+class TwigExtension extends GravExtension
+{
+}