pkg/async: fix spelling in doc comments

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.**
 ///
-/// If the `StreamGroup` is construced using [new StreamGroup], [stream] will be
+/// If the `StreamGroup` is constructed using [new StreamGroup], [stream] will be
 /// single-subscription. In this case, if [stream] is paused or canceled, all
 /// streams in the group will likewise be paused or canceled, respectively.
 ///
-/// If the `StreamGroup` is construced using [new StreamGroup.broadcast],
+/// If the `StreamGroup` is constructed using [new StreamGroup.broadcast],
 /// [stream] will be a broadcast stream. In this case, the streams in the group
 /// will never be paused and single-subscription streams in the group will never
 /// be canceled. **Note that single-subscription streams in a broadcast group
 /// may drop events if a listener is added and later removed.** Broadcast
 /// streams in the group will be canceled once [stream] has no listeners, and
 /// will be listened to again once [stream] has listeners.
 ///
 /// [stream] won't close until [close] is called on the group *and* every stream
 /// in the group closes.
 class StreamGroup<T> implements Sink<Stream<T>> {
@@ skipping 218 matching lines @@
 
   /// The name of the state.
   ///
   /// Used for debugging.
   final String name;
 
   const _StreamGroupState(this.name);
 
   String toString() => name;
 }