[gnome-shell] messageList: Add missing import

[Florian Müllner <fmuellner src gnome org>]

commit ede0bf2d88f104d341c5d4a224ecdbc97ae36a46
Author: Florian Müllner <fmuellner gnome org>
Date:   Mon Feb 22 19:27:09 2016 +0100

    messageList: Add missing import
    
    We lost that when code was split out from calendar.js ...

 js/ui/messageList.js |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/js/ui/messageList.js b/js/ui/messageList.js
index 57c829a..325f5a3 100644
--- a/js/ui/messageList.js
+++ b/js/ui/messageList.js
@@ -1,5 +1,6 @@
 const Atk = imports.gi.Atk;
 const Clutter = imports.gi.Clutter;
+const Gio = imports.gi.Gio;
 const GLib = imports.gi.GLib;
 const GObject = imports.gi.GObject;
 const Lang = imports.lang;