Fix race condition in FakeAsync timeout test (#17)
Fix race condition in FakeAsync timeout test (#17)

Dart SDK commit 6255638cd0623b3aa41596b98f4584876f6b8822 introduced
changes to stream subscription cancellation. cancelOnError was
irrelevant to the periodic and timeout tests.
QuiverDart/quiver_async,googlearchive/quiver_async,QuiverDart/quiver_async,googlearchive/quiver_async