[gnome-documents] build: Update to latest libgd

[Debarshi Ray <debarshir src gnome org>]

commit 348dec26c77ecaff0240009afbd7f4f74f877a63
Author: Debarshi Ray <debarshir gnome org>
Date:   Thu May 11 11:44:31 2017 +0200

    build: Update to latest libgd
    
    Silences a deprecation warning due to the use of gtk_paint_spinner.

 libgd |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgd b/libgd
index 63d1488..3afb334 160000
--- a/libgd
+++ b/libgd
@@ -1 +1 @@
-Subproject commit 63d1488b3bcea686e85dd7273365861eacbe8442
+Subproject commit 3afb334ed1d87580df0adf34c8ed6c31e5d3d667