Fix an outdated method call in example code for oauth2.

BUG=7675

Review URL: https://codereview.chromium.org//12787015

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@20341 260f80e4-7a28-3924-810f-c04153c831b5
diff --git a/lib/oauth2.dart b/lib/oauth2.dart
index 4dfaadd..7fdb205 100644
--- a/lib/oauth2.dart
+++ b/lib/oauth2.dart
@@ -56,7 +56,7 @@
 ///       // If the OAuth2 credentials have already been saved from a previous
 ///       // run, we just want to reload them.
 ///       if (exists) {
-///         return credentialsFile.readAsText().then((json) {
+///         return credentialsFile.readAsString().then((json) {
 ///           var credentials = new oauth2.Credentials.fromJson(json);
 ///           return new oauth2.Client(identifier, secret, credentials);
 ///         });