[gnome-boxes] Add missing translation marker

[Christophe Fergeau <teuf src gnome org>]

commit 810776150150a7d74505517694656c03ca6475a3
Author: Christophe Fergeau <cfergeau redhat com>
Date:   Wed Dec 11 14:22:07 2013 +0100

    Add missing translation marker
    
    During the port away from stock items, one of the newly added string was
    not marked for translation.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=720253

 src/app.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/app.vala b/src/app.vala
index 2c5022d..1014503 100644
--- a/src/app.vala
+++ b/src/app.vala
@@ -863,7 +863,7 @@ private class Boxes.App: Boxes.UI {
             }
         };
 
-        notificationbar.display_for_action (message, "_Undo", (owned) undo, (owned) really_remove);
+        notificationbar.display_for_action (message, _("_Undo"), (owned) undo, (owned) really_remove);
     }
 
     private bool on_key_pressed (Widget widget, Gdk.EventKey event) {