Laravel 5.6 updates

Travis config update

Removed HHVM script as Laravel no longer support HHVM after releasing 5.3

vendor/symfony/var-dumper/Dumper/ContextProvider/ContextProviderInterface.php

@@ -0,0 +1,25 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\VarDumper\Dumper\ContextProvider;
+
+/**
+ * Interface to provide contextual data about dump data clones sent to a server.
+ *
+ * @author Maxime Steinhausser <maxime.steinhausser@gmail.com>
+ */
+interface ContextProviderInterface
+{
+    /**
+     * @return array|null Context data or null if unable to provide any context
+     */
+    public function getContext(): ?array;
+}