pkg/path: fixed tiny doc bug

path.dirname('path/to') returns 'path', not 'to'

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//19492003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/path@25120 260f80e4-7a28-3924-810f-c04153c831b5
diff --git a/lib/path.dart b/lib/path.dart
index 25ce0e6..1d83c00 100644
--- a/lib/path.dart
+++ b/lib/path.dart
@@ -109,7 +109,7 @@
 /// Gets the part of [path] before the last separator.
 ///
 ///     path.dirname('path/to/foo.dart'); // -> 'path/to'
-///     path.dirname('path/to');          // -> 'to'
+///     path.dirname('path/to');          // -> 'path'
 ///
 /// Trailing separators are ignored.
 ///