cleanup: Require "dangling" commas

Since ES5, trailing commas in arrays and object literals are valid.
We generally haven't used them so far, but they are actually a good
idea, as they make additions and removals in diffs much cleaner.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/805

js/misc/gnomeSession.js

@@ -11,7 +11,7 @@ var PresenceStatus = {
     AVAILABLE: 0,
     INVISIBLE: 1,
     BUSY: 2,
-    IDLE: 3
+    IDLE: 3,
 };
 
 var PresenceProxy = Gio.DBusProxy.makeProxyWrapper(PresenceIface);