keyboard: Add back constructor parameter

This was accidentally dropped in commit bacfdbbb03.

Spotted by eslint.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/375

js/ui/keyboard.js

@@ -232,7 +232,7 @@ var LanguageSelectionPopup = class extends PopupMenu.PopupMenu {
 };
 
 var Key = class Key {
-    constructor(key) {
+    constructor(key, extendedKeys) {
         this.key = key || "";
         this.keyButton = this._makeKey(this.key);