Laravel 5.6 updates

Travis config update

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

vendor/symfony/http-kernel/DependencyInjection/ResettableServicePass.php

@@ -25,7 +25,7 @@ class ResettableServicePass implements CompilerPassInterface
 {
     private $tagName;
 
-    public function __construct($tagName = 'kernel.reset')
+    public function __construct(string $tagName = 'kernel.reset')
     {
         $this->tagName = $tagName;
     }