added an empty abstract inner hit

src/InnerHit/AbstractInnerHit.php

+<?php
+
+/*
+ * This file is part of the ONGR package.
+ *
+ * (c) NFQ Technologies UAB <info@nfq.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace ONGR\ElasticsearchDSL\InnerHit;
+
+use ONGR\ElasticsearchDSL\BuilderInterface;
+
+/**
+ * AbstractAggregation class.
+ */
+abstract class AbstractInnerHit implements BuilderInterface
+{
+    /**
+     * {@inheritdoc}
+     */
+    abstract public function toArray();
+
+    /**
+     * {@inheritdoc}
+     */
+    abstract public function getType();
+}