[e2e] fix flutter driver code snippet in readme and improve formattin…

…g of code snippets (flutter#2549)

* [e2e] fix flutter driver code snippet in readme and improve formatting

packages/e2e/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.2.4+3
+
+* Fixed code snippet in the readme under the "Using Flutter driver to run tests" section.
+
 ## 0.2.4+2
 
 * Make the pedantic dev_dependency explicit.

packages/e2e/README.md

@@ -41,12 +41,15 @@ Note that the tests don't use the `FlutterDriver` API, they use `testWidgets` in
 
 Put the a file named `<package_name>_e2e_test.dart` in the app' `test_driver` directory:
 
-```
+```dart
+import 'dart:async';
+import 'dart:io';
 import 'package:flutter_driver/flutter_driver.dart';
 
 Future<void> main() async {
   final FlutterDriver driver = await FlutterDriver.connect();
-  await driver.requestData(null, timeout: const Duration(minutes: 1));
+  final String result =
+      await driver.requestData(null, timeout: const Duration(minutes: 1));
   await driver.close();
   exit(result == 'pass' ? 0 : 1);
 }
@@ -73,7 +76,7 @@ Create an instrumentation test file in your application's
 com, example, and myapp with values from your app's package name). You can name
 this test file MainActivityTest.java or another name of your choice.
 
-```
+```java
 package com.example.myapp;
 
 import androidx.test.rule.ActivityTestRule;

packages/e2e/pubspec.yaml

@@ -1,6 +1,6 @@
 name: e2e
 description: Runs tests that use the flutter_test API as integration tests.
-version: 0.2.4+2
+version: 0.2.4+3
 homepage: https://github.com/flutter/plugins/tree/master/packages/e2e
 
 environment: