text/template: fix typo in package comment
text/template: fix typo in package comment

Fixes issue 3383.

R=iant, bradfitz
CC=golang-dev
http://codereview.appspot.com/5891045
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go