Laravel 5.6 updates

Travis config update

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

vendor/symfony/http-kernel/ControllerMetadata/ArgumentMetadata.php

@@ -25,15 +25,7 @@ class ArgumentMetadata
     private $defaultValue;
     private $isNullable;
 
-    /**
-     * @param string $name
-     * @param string $type
-     * @param bool   $isVariadic
-     * @param bool   $hasDefaultValue
-     * @param mixed  $defaultValue
-     * @param bool   $isNullable
-     */
-    public function __construct($name, $type, $isVariadic, $hasDefaultValue, $defaultValue, $isNullable = false)
+    public function __construct(string $name, ?string $type, bool $isVariadic, bool $hasDefaultValue, $defaultValue, bool $isNullable = false)
     {
         $this->name = $name;
         $this->type = $type;