Laravel 5.6 updates

Travis config update

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

vendor/symfony/console/Descriptor/ApplicationDescription.php

@@ -43,12 +43,7 @@ class ApplicationDescription
      */
     private $aliases;
 
-    /**
-     * @param Application $application
-     * @param string|null $namespace
-     * @param bool        $showHidden
-     */
-    public function __construct(Application $application, $namespace = null, $showHidden = false)
+    public function __construct(Application $application, string $namespace = null, bool $showHidden = false)
     {
         $this->application = $application;
         $this->namespace = $namespace;
@@ -123,10 +118,7 @@ class ApplicationDescription
         }
     }
 
-    /**
-     * @return array
-     */
-    private function sortCommands(array $commands)
+    private function sortCommands(array $commands): array
     {
         $namespacedCommands = array();
         $globalCommands = array();