[vala] vapi: Update GIR-based bindings

[Rico Tzschichholz <ricotz src gnome org>]

commit 93105106e5644f9feca9bbbe29eb007ca648d4a8
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Tue May 1 12:44:43 2018 +0200

    vapi: Update GIR-based bindings

 vapi/gdk-pixbuf-2.0.vapi |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/vapi/gdk-pixbuf-2.0.vapi b/vapi/gdk-pixbuf-2.0.vapi
index 54efc24..abb073d 100644
--- a/vapi/gdk-pixbuf-2.0.vapi
+++ b/vapi/gdk-pixbuf-2.0.vapi
@@ -13,8 +13,8 @@ namespace Gdk {
                public static int calculate_rowstride (Gdk.Colorspace colorspace, bool has_alpha, int 
bits_per_sample, int width, int height);
                public void composite (Gdk.Pixbuf dest, int dest_x, int dest_y, int dest_width, int 
dest_height, double offset_x, double offset_y, double scale_x, double scale_y, Gdk.InterpType interp_type, 
int overall_alpha);
                public void composite_color (Gdk.Pixbuf dest, int dest_x, int dest_y, int dest_width, int 
dest_height, double offset_x, double offset_y, double scale_x, double scale_y, Gdk.InterpType interp_type, 
int overall_alpha, int check_x, int check_y, int check_size, uint32 color1, uint32 color2);
-               public Gdk.Pixbuf composite_color_simple (int dest_width, int dest_height, Gdk.InterpType 
interp_type, int overall_alpha, int check_size, uint32 color1, uint32 color2);
-               public Gdk.Pixbuf copy ();
+               public Gdk.Pixbuf? composite_color_simple (int dest_width, int dest_height, Gdk.InterpType 
interp_type, int overall_alpha, int check_size, uint32 color1, uint32 color2);
+               public Gdk.Pixbuf? copy ();
                public void copy_area (int src_x, int src_y, int width, int height, Gdk.Pixbuf dest_pixbuf, 
int dest_x, int dest_y);
                [Version (since = "2.36")]
                public bool copy_options (Gdk.Pixbuf dest_pixbuf);