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/runDialog.js

@@ -249,7 +249,7 @@ class RunDialog extends ModalDialog.ModalDialog {
                 onComplete: () => {
                     parentActor.set_height(-1);
                     this._errorBox.show();
-                }
+                },
             });
         }
     }