[bindings] Replace deprecated allow-none with optional and nullable
diff --git a/src/hb-unicode.cc b/src/hb-unicode.cc
index d59dfb2..fc19006 100644
--- a/src/hb-unicode.cc
+++ b/src/hb-unicode.cc
@@ -157,7 +157,7 @@
 
 /**
  * hb_unicode_funcs_create: (Xconstructor)
- * @parent: (allow-none):
+ * @parent: (nullable):
  *
  * 
  *