go-tour: use moved playground package
go-tour: use moved playground package

Fixes  issue 104 .

R=golang-dev, adg
CC=golang-dev
https://codereview.appspot.com/11977043

Committer: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

BenjaminTsai/go-tour-zh-tw,BenjaminTsai/go-tour-zh-tw