[gnome-photos] Update to latest libgd

[Debarshi Ray <debarshir src gnome org>]

commit 3ecfd62cb96441c03f93b2ea63327392432b4ac9
Author: Debarshi Ray <debarshir gnome org>
Date:   Thu Feb 23 09:40:40 2017 +0100

    Update to latest libgd
    
    The "content-tile" style class has been renamed to "tile".

 libgd |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgd b/libgd
index 1bd7f34..97a852c 160000
--- a/libgd
+++ b/libgd
@@ -1 +1 @@
-Subproject commit 1bd7f34a58f11f4bdebcbe5ca3371b89c6c2c83c
+Subproject commit 97a852cdf3d37776f9c98f730d7dcbbe995bdeb7