[gnome-photos] Update to latest libgd

[Debarshi Ray <debarshir src gnome org>]

commit c48df565560a950b51a2c9ed0d3aecd10733f562
Author: Debarshi Ray <debarshir gnome org>
Date:   Mon Oct 8 12:37:13 2018 +0200

    Update to latest libgd
    
    Silence some deprecation warnings with GLib 2.57.2 due to
    g_type_class_add_private.

 subprojects/libgd | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/subprojects/libgd b/subprojects/libgd
index 039eff81..4c928b61 160000
--- a/subprojects/libgd
+++ b/subprojects/libgd
@@ -1 +1 @@
-Subproject commit 039eff81546b1076bcad5eab5ee6bc37e702e0a5
+Subproject commit 4c928b6101c748a96001d673c9e6a7aeb74722e0