Notes have a system field

Author: Jordan Hoff

lib/Gitlab/Model/Note.php

@@ -12,6 +12,7 @@
  * @property-read string $parent_type
  * @property-read Issue|MergeRequest $parent
  * @property-read string $attachment
+ * @property-read bool $system
  */
 class Note extends AbstractModel
 {
@@ -26,7 +27,8 @@ class Note extends AbstractModel
         'updated_at',
         'parent_type',
         'parent',
-        'attachment'
+        'attachment',
+        'system'
     );
 
     /**