status/keyboard: use correct style class name to fix menu highlight

The keyboard status item doesn't derive from SystemStatusButton, since
it doesn't use an icon. But this meant it wasn't getting the right
class name, and so was using the full-width menu title highlight
rather than the small one. Fix that.

js/ui/status/keyboard.js

@@ -53,6 +53,7 @@ XKBIndicator.prototype = {
         this._container.connect('get-preferred-height', Lang.bind(this, this._containerGetPreferredHeight));
         this._container.connect('allocate', Lang.bind(this, this._containerAllocate));
         this.actor.set_child(this._container);
+        this.actor.add_style_class_name('panel-status-button');
 
         this._iconActor = new St.Icon({ icon_name: 'keyboard', icon_type: St.IconType.SYMBOLIC, style_class: 'system-status-icon' });
         this._container.add_actor(this._iconActor);