Fixes a minor typo in the documentation of the StreamTransformer class.

Change-Id: I4d1142d14cf01d2b8c04d6bf41f9bac7c86c0d5a
Reviewed-on: https://dart-review.googlesource.com/68880
Reviewed-by: Dmitry Stefantsov <dmitryas@google.com>
Commit-Queue: Daniel Hillerström <hillerstrom@google.com>
diff --git a/sdk/lib/async/stream.dart b/sdk/lib/async/stream.dart
index a5a0055..33a7ac4 100644
--- a/sdk/lib/async/stream.dart
+++ b/sdk/lib/async/stream.dart
@@ -2008,7 +2008,7 @@
   Stream<T> bind(Stream<S> stream);
 
   /**
-   * Provides a `StreamTrasformer<RS, RT>` view of this stream transformer.
+   * Provides a `StreamTransformer<RS, RT>` view of this stream transformer.
    *
    * The resulting transformer will check at run-time that all data events
    * of the stream it transforms are actually instances of [S],