[wing/wip/nacho/poll-stream] It is derivable

[Ignacio Casal Quinteiro <icq src gnome org>]

commit f34dd86439f5d64dfed5fa52bd5224747d13a5ee
Author: Ignacio Casal Quinteiro <qignacio amazon com>
Date:   Wed Nov 28 16:48:18 2018 +0100

    It is derivable

 wing/winginputstream.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/wing/winginputstream.h b/wing/winginputstream.h
index 7c09b94..e0db204 100644
--- a/wing/winginputstream.h
+++ b/wing/winginputstream.h
@@ -36,7 +36,7 @@ G_BEGIN_DECLS
  * Implements #GInputStream for reading from selectable Windows file handles
  **/
 WING_AVAILABLE_IN_ALL
-G_DECLARE_FINAL_TYPE (WingInputStream, wing_input_stream, WING, INPUT_STREAM, GInputStream)
+G_DECLARE_DERIVABLE_TYPE (WingInputStream, wing_input_stream, WING, INPUT_STREAM, GInputStream)
 
 struct _WingInputStreamClass
 {