[gnome-documents] libgd: Bump libgd for GTK+ 3.19 fixes

[Bastien Nocera <hadess src gnome org>]

commit d15a1f21535301ec47712b3bb574497b87dcd971
Author: Bastien Nocera <hadess hadess net>
Date:   Tue Nov 24 15:53:35 2015 +0100

    libgd: Bump libgd for GTK+ 3.19 fixes
    
    This fixes warnings running with newer GTK+ versions.

 libgd |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgd b/libgd
index f2b8fb3..7c12355 160000
--- a/libgd
+++ b/libgd
@@ -1 +1 @@
-Subproject commit f2b8fb3acbee7568f7cb864dd58da42c06412cb3
+Subproject commit 7c1235591c4aa866b28c8b8dabdcb3b9084c5763