Laravel 5.6 updates

Travis config update

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

vendor/symfony/var-dumper/Tests/Caster/CasterTest.php

@@ -151,9 +151,6 @@ class CasterTest extends TestCase
         );
     }
 
-    /**
-     * @requires PHP 7.0
-     */
     public function testAnonymousClass()
     {
         $c = eval('return new class extends stdClass { private $foo = "foo"; };');