[gnome-boxes] libgd: Update to latest git master

[Zeeshan Ali Khattak <zeeshanak src gnome org>]

commit e638896ac01323f9dbae4d63b20cc29c2a72ca65
Author: Zeeshan Ali (Khattak) <zeeshanak gnome org>
Date:   Mon Dec 7 18:01:29 2015 +0000

    libgd: Update to latest git master
    
    Otherwise, we get warnings on console against latest gtk+.

 libgd |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgd b/libgd
index 241f3d5..7c12355 160000
--- a/libgd
+++ b/libgd
@@ -1 +1 @@
-Subproject commit 241f3d59be499bc1aa97704050e62eaef69a0d51
+Subproject commit 7c1235591c4aa866b28c8b8dabdcb3b9084c5763