[gnome-nibbles] Fix window size increasing with GTK+ 3.20

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 8bd7253337af8f1b3afaed8c965399bfb589c6af
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Sun Feb 14 16:47:58 2016 -0600

    Fix window size increasing with GTK+ 3.20

 src/gnome-nibbles.vala |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)
---
diff --git a/src/gnome-nibbles.vala b/src/gnome-nibbles.vala
index dc5ed2a..2b13def 100644
--- a/src/gnome-nibbles.vala
+++ b/src/gnome-nibbles.vala
@@ -253,8 +253,7 @@ public class Nibbles : Gtk.Application
     {
         if (is_maximized || is_tiled)
             return;
-        window_width = allocation.width;
-        window_height = allocation.height;
+        window.get_size (out window_width, out window_height);
     }
 
     private bool window_state_event_cb (Gdk.EventWindowState event)