[gnome-photos] Update to latest libgd

[Debarshi Ray <debarshir src gnome org>]

commit 3545f478e2b534c34f94b17eacf77b5b94550e53
Author: Debarshi Ray <debarshir gnome org>
Date:   Thu Dec 15 10:51:20 2016 +0100

    Update to latest libgd
    
    Fix the size and offset of the counter icon when dragging and dropping
    multiple items on HiDpi displays.

 libgd |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgd b/libgd
index a6f2d75..78a910b 160000
--- a/libgd
+++ b/libgd
@@ -1 +1 @@
-Subproject commit a6f2d754203582adedb2a5a896a31ce5b73e05d1
+Subproject commit 78a910b0440854f97af80a9b0bd8cb4a3d3a06e1