fix(step): fixed tap back button step

lib/src/flutter/steps/when_tap_the_back_button_step.dart

@@ -10,13 +10,13 @@ import 'package:gherkin/gherkin.dart';
 ///   `When I tap the back button"`
 ///   `When I tap the back element"`
 ///   `When I tap the back widget"`
-class WhenTapBackButtonWidget extends When1WithWorld<String, FlutterWorld> {
+class WhenTapBackButtonWidget extends WhenWithWorld<FlutterWorld> {
   @override
   RegExp get pattern =>
       RegExp(r"I tap the back [button|element|widget]");
 
   @override
-  Future<void> executeStep(String key) async {
+  Future<void> executeStep() async {
     await FlutterDriverUtils.tap(
       world.driver,
       find.pageBack(),