Modernize the package's style.

lib/src/single_subscription_transformer.dart

 // Copyright (c) 2016, 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.single_subscription_transformer;
-
 import 'dart:async';
 
 /// A transformer that converts a broadcast stream into a single-subscription
 /// stream.
 ///
 /// This buffers the broadcast stream's events, which means that it starts
 /// listening to a stream as soon as it's bound.
 class SingleSubscriptionTransformer<S, T> implements StreamTransformer<S, T> {
   const SingleSubscriptionTransformer();
 
   Stream<T> bind(Stream<S> stream) {
     var subscription;
     var controller = new StreamController(sync: true,
         onCancel: () => subscription.cancel());
     subscription = stream.listen(controller.add,
         onError: controller.addError, onDone: controller.close);
     return controller.stream;
   }
 }