[gnome-documents] build: Update to latest libgd

[Debarshi Ray <debarshir src gnome org>]

commit a60d5c16e6cc9e144c32530117d79252cbdcd04a
Author: Debarshi Ray <debarshir gnome org>
Date:   Fri Oct 30 16:50:20 2015 +0100

    build: Update to latest libgd
    
    Silences a compiler warning.

 libgd |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgd b/libgd
index ed6c8f3..bf0b5c9 160000
--- a/libgd
+++ b/libgd
@@ -1 +1 @@
-Subproject commit ed6c8f3667b67ac284933a3d03faa34b5948bf52
+Subproject commit bf0b5c96a6b2f4b039fc12c2cef7729fc7cb6ecf