delay: fix example in doc comment

Change-Id: I3732eb1ff659cd1079248d4cecfefaeeab5c192d
diff --git a/delay/delay.go b/delay/delay.go
index 6d628fc..5e9b8e0 100644
--- a/delay/delay.go
+++ b/delay/delay.go
@@ -137,7 +137,7 @@
 //   err := f.Call(c, ...)
 // is equivalent to
 //   t, _ := f.Task(...)
-//   err := taskqueue.Add(c, t, "")
+//   _, err := taskqueue.Add(c, t, "")
 func (f *Function) Call(c context.Context, args ...interface{}) error {
 	t, err := f.Task(args...)
 	if err != nil {