go-tour: update default cc to golang-codereviews mailing list
go-tour: update default cc to golang-codereviews mailing list

LGTM=minux.ma
R=golang-codereviews, minux.ma
CC=golang-codereviews
https://codereview.appspot.com/67760043

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