bytes: Fix missing godoc punctuation.
bytes: Fix missing godoc punctuation.

R=golang-dev, rsc
CC=golang-dev
https://codereview.appspot.com/7067047

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