doc/codelab: correct typo.
doc/codelab: correct typo.

s/Sprintf/Fprintf/

R=golang-dev, rsc
CC=adg, golang-dev
http://codereview.appspot.com/4519053

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go