[gnome-documents] build: update to latest libgd

[Carl-Anton Ingmarsson <carlantoni src gnome org>]

commit 0c748e4eeab67e6ab4d26fdb52abe274090036cd
Author: Carl-Anton Ingmarsson <ca ingmarsson gmail com>
Date:   Fri Sep 6 18:07:48 2013 +0200

    build: update to latest libgd
    
    Fixes crash when window is closed.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=707619

 libgd |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgd b/libgd
index 391746c..62f9b8b 160000
--- a/libgd
+++ b/libgd
@@ -1 +1 @@
-Subproject commit 391746cb369ec7bf2bd850c58c1ee2501041214e
+Subproject commit 62f9b8b92599b38d986bd26d5780edd400d318c9