[gtk+] Add a forgotten deprecation

[Matthias Clasen <matthiasc src gnome org>]

commit 172093db8c0e6602c09393b10b7156d600955975
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Apr 30 16:29:16 2016 -0400

    Add a forgotten deprecation
    
    gdk_display_get_screen is marked as deprecated in the docs.

 gdk/gdkdisplay.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gdk/gdkdisplay.h b/gdk/gdkdisplay.h
index 197b95f..86dece7 100644
--- a/gdk/gdkdisplay.h
+++ b/gdk/gdkdisplay.h
@@ -52,7 +52,7 @@ const gchar * gdk_display_get_name         (GdkDisplay *display);
 
 GDK_DEPRECATED_IN_3_10
 gint        gdk_display_get_n_screens      (GdkDisplay  *display);
-GDK_AVAILABLE_IN_ALL
+GDK_DEPRECATED_IN_3_20
 GdkScreen * gdk_display_get_screen         (GdkDisplay  *display,
                                             gint         screen_num);
 GDK_AVAILABLE_IN_ALL