[auth] Update typescript

lib/index.d.ts

@@ -637,6 +637,11 @@ declare module "react-native-firebase" {
          */
         currentUser: User | null
 
+        /**
+         * Gets/Sets the language for the app instance
+         */
+        languageCode: string | null;
+
         /**
          * Listen for changes in the users auth state (logging in and out).
          * This method returns a unsubscribe function to stop listening to events.
@@ -705,6 +710,11 @@ declare module "react-native-firebase" {
          */
         signOut(): Promise<void>
 
+        /**
+         * Sets the language for the auth instance to the device language
+         */
+        useDeviceLanguage(): void
+
         [key: string]: any;
       }
     }