Fixing emacs-related comments

Change-Id: Ia9be75af500e72faa8fa2119793acc6dc693bba2
diff --git a/osx/sparkle-auto-update.mm b/osx/sparkle-auto-update.mm
index a515a79..a3a9b20 100644
--- a/osx/sparkle-auto-update.mm
+++ b/osx/sparkle-auto-update.mm
@@ -1,4 +1,4 @@
-/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
+/* -*- Mode: objc; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
 /*
  * @copyright See LICENCE for copyright and license information.
  *