Fix a typo from e05cfca.

test/descriptor.dart

 // Copyright (c) 2013, 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.
 
 /// Pub-specific scheduled_test descriptors.
 library descriptor;
 
 import "dart:io" show File;
 
 import 'package:oauth2/oauth2.dart' as oauth2;
@@ skipping 175 matching lines @@
 }
 
 /// Describes the application directory, containing only a pubspec specifying
 /// the given [dependencies].
 DirectoryDescriptor appDir([Map dependencies]) =>
   dir(appPath, [appPubspec(dependencies)]);
 
 /// Describes a `.packages` file.
 ///
 /// [dependencies] maps package names to strings describing where the packages
-/// are located on disk. If the strings are sematnic versions, then the packages
+/// are located on disk. If the strings are semantic versions, then the packages
 /// are located in the system cache; otherwise, the strings are interpreted as
 /// relative `file:` URLs.
 ///
 /// Validation checks that the `.packages` file exists, has the expected
 /// entries (one per key in [dependencies]), each with a path that contains
 /// either the version string (for a reference to the pub cache) or a
 /// path to a path dependency, relative to the application directory.
 Descriptor packagesFile([Map dependencies]) =>
   new PackagesFileDescriptor(dependencies);