fix: Refactor for pull request dart-lang#688

Author: myConsciousness

lib/src/base_response.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:universal_io/io.dart';
+import 'dart:io';
 
 import 'base_client.dart';
 import 'base_request.dart';

pubspec.yaml

@@ -11,7 +11,6 @@ dependencies:
   http_parser: ^4.0.0
   meta: ^1.3.0
   path: ^1.8.0
-  universal_io: ^2.0.4
 
 dev_dependencies:
   fake_async: ^1.2.0

test/response_test.dart

@@ -113,7 +113,7 @@ void main() {
     });
 
     expect(response.cookies.length, 1);
-    expect(response.cookies[0].name, 'AWSALB');
-    expect(response.cookies[0].value, 'AWSALB_TEST');
+    expect(response.cookies.first.name, 'AWSALB');
+    expect(response.cookies.first.value, 'AWSALB_TEST');
   });
 }