Laravel 5.6 updates

Travis config update

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

vendor/symfony/http-kernel/Exception/HttpException.php

@@ -21,7 +21,7 @@ class HttpException extends \RuntimeException implements HttpExceptionInterface
     private $statusCode;
     private $headers;
 
-    public function __construct($statusCode, $message = null, \Exception $previous = null, array $headers = array(), $code = 0)
+    public function __construct(int $statusCode, string $message = null, \Exception $previous = null, array $headers = array(), ?int $code = 0)
     {
         $this->statusCode = $statusCode;
         $this->headers = $headers;