[gnome-calendar] build: updated libgd to latest

[Erick Pérez Castellanos <erickpc src gnome org>]

commit 318cd4dd3387fb7f710e115911a6e383d3cceaa5
Author: Erick Pérez Castellanos <erick red gmail com>
Date:   Tue Jun 18 10:02:17 2013 -0400

    build: updated libgd to latest
    
    Fixed build warning

 libgd |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgd b/libgd
index 5f75e01..a1f7543 160000
--- a/libgd
+++ b/libgd
@@ -1 +1 @@
-Subproject commit 5f75e01e74235e2a503356e2198599cb1105b7dc
+Subproject commit a1f754372958b6d67e4116e8b7da8ef702dd1668