package barback: Update the comment style generic syntax.

lib/src/utils/cancelable_future.dart

Index: lib/src/utils/cancelable_future.dart
diff --git a/lib/src/utils/cancelable_future.dart b/lib/src/utils/cancelable_future.dart
index aaa5e3651fca3c283e8c422b8c98418f932090a9..78a391fae4a7bf565671e018937d5d131fb53825 100644
--- a/lib/src/utils/cancelable_future.dart
+++ b/lib/src/utils/cancelable_future.dart
@@ -29,8 +29,7 @@ class CancelableFuture<T> implements Future<T> {
   Stream<T> asStream() => _completer.future.asStream();
   Future<T> catchError(Function onError, {bool test(Object error)}) =>
       _completer.future.catchError(onError, test: test);
-  Future/*<S>*/ then/*<S>*/(/*=FutureOr<S>*/ onValue(T value),
-          {Function onError}) =>
+  Future<S> then<S>(FutureOr<S> onValue(T value), {Function onError}) =>
       _completer.future.then(onValue, onError: onError);
   Future<T> whenComplete(action()) => _completer.future.whenComplete(action);
   Future<T> timeout(Duration timeLimit, {void onTimeout()}) =>