Modernize the package's style.

lib/src/stream_group.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS 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 async.stream_group;
-
 import 'dart:async';
 
 /// A collection of streams whose events are unified and sent through a central
 /// stream.
 ///
 /// Both errors and data events are forwarded through [stream]. The streams in
 /// the group won't be listened to until [stream] has a listener. **Note that
 /// this means that events emitted by broadcast streams will be dropped until
 /// [stream] has a listener.**
 ///
@@ skipping 233 matching lines @@
 
   /// The name of the state.
   ///
   /// Used for debugging.
   final String name;
 
   const _StreamGroupState(this.name);
 
   String toString() => name;
 }