Fix pub test that broke with changes in dart:convert

sdk/lib/_internal/pub/test/serve/404_page_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.file
 // 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.
 
 library pub_tests;
 
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
@@ skipping 21 matching lines @@
     endPubServe();
   });
 
   integration("the 404 page describes the error", () {
     pubServe();
 
     scheduleRequest("packages").then((response) {
       expect(response.statusCode, equals(404));
 
       // Should mention the asset that can't be found.
-      expect(response.body, contains('"/packages"'));
+      expect(response.body, contains('"/packages"'));
     });
 
     endPubServe();
   });
 }