pkg/async: fix spelling in doc comments

lib/src/stream_group.dart

Index: lib/src/stream_group.dart
diff --git a/lib/src/stream_group.dart b/lib/src/stream_group.dart
index 0147787880462b1824142aef45df54258df74e7f..d99f5151467855dc97fb3f92d804b53c21c78a6a 100644
--- a/lib/src/stream_group.dart
+++ b/lib/src/stream_group.dart
@@ -14,11 +14,11 @@ import 'dart:async';
 /// 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