[gnome-documents] build: Update to latest libgd

[Debarshi Ray <debarshir src gnome org>]

commit 5c0eeec06920ce50d9678d5586487a347cfe39b9
Author: Debarshi Ray <debarshir gnome org>
Date:   Mon May 1 21:32:08 2017 +0200

    build: Update to latest libgd
    
    It gives us some GObject modernizations, fixes to the selection mode
    and drag-n-drop counter on HiDpi, the new entry-tag CSS style class
    from Adwaita and silences deprecation warnings from the
    GdkDeviceManager API.

 libgd |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgd b/libgd
index 6eefe0e..63d1488 160000
--- a/libgd
+++ b/libgd
@@ -1 +1 @@
-Subproject commit 6eefe0edd03bfedb65e6fdefe7cde9f3a3da437f
+Subproject commit 63d1488b3bcea686e85dd7273365861eacbe8442