[gnome-contacts] App: Disambiguate Gtk.Dialog

[Niels De Graef <nielsdg src gnome org>]

commit 3820a582eae7235a69ee392823a77a052e5d962d
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Wed Jan 16 14:24:51 2019 +0100

    App: Disambiguate Gtk.Dialog
    
    Hdy.Dialog now exists on libhandy master.

 src/contacts-app.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/contacts-app.vala b/src/contacts-app.vala
index c3edf6f..2ae52e5 100644
--- a/src/contacts-app.vala
+++ b/src/contacts-app.vala
@@ -110,7 +110,7 @@ public class Contacts.App : Gtk.Application {
   }
 
   public void change_address_book () {
-    var dialog = new Dialog.with_buttons (_("Change Address Book"),
+    var dialog = new Gtk.Dialog.with_buttons (_("Change Address Book"),
                                          (Window) window,
                                          DialogFlags.MODAL |
                                          DialogFlags.DESTROY_WITH_PARENT |