Laravel 5.6 updates

Travis config update

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

vendor/symfony/http-foundation/StreamedResponse.php

@@ -35,7 +35,7 @@ class StreamedResponse extends Response
      * @param int           $status   The response status code
      * @param array         $headers  An array of response headers
      */
-    public function __construct(callable $callback = null, $status = 200, $headers = array())
+    public function __construct(callable $callback = null, int $status = 200, array $headers = array())
     {
         parent::__construct(null, $status, $headers);