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/ui/accessDialog.js

@@ -13,7 +13,7 @@ const AccessIface = loadInterfaceXML('org.freedesktop.impl.portal.Access');
 var DialogResponse = {
     OK: 0,
     CANCEL: 1,
-    CLOSED: 2
+    CLOSED: 2,
 };
 
 var AccessDialog = GObject.registerClass(