go-tour: add missing delete/error/rune predeclared identifier for Syntax-Highlighting
go-tour: add missing delete/error/rune predeclared identifier for Syntax-Highlighting

LGTM=adg
R=golang-codereviews, bradfitz, adg
CC=golang-codereviews
https://codereview.appspot.com/99040045

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

Go-zh/tour-old,Go-zh/tour-old,minux/go-tour-zh,minux/go-tour-zh