Remove unused dart:async imports. (#50)
As of Dart 2.1, Future/Stream have been exported from dart:core.
diff --git a/test/message_grouper_test.dart b/test/message_grouper_test.dart
index 8843b69..aa0570b 100644
--- a/test/message_grouper_test.dart
+++ b/test/message_grouper_test.dart
@@ -2,7 +2,6 @@
// 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 'dart:async';
import 'dart:io';
import 'package:test/test.dart';
