[StTable] fix x-align/y-align properties to be StAlign, not double

This puts it in sync with StBin and StBoxLayout

https://bugzilla.gnome.org/show_bug.cgi?id=609848

js/ui/messageTray.js

@@ -220,7 +220,7 @@ Notification.prototype = {
             let box = new St.BoxLayout({ name: 'notification-actions' });
             this.addActor(box, { x_expand: false,
                                  x_fill: false,
-                                 x_align: 1.0 });
+                                 x_align: St.Align.END });
             this._actionBox = box;
         }