go/ast: fix typo
go/ast: fix typo

R=golang-dev, r, bradfitz
CC=golang-dev
http://codereview.appspot.com/5543056

Committer: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go