gotour: use vendored copy of golang.org/x/tour packages
gotour: use vendored copy of golang.org/x/tour packages

Note: we should not change the import path of those packages to
github.com/Go-zh, otherwise local gotour users will be forced
to use a different import statement as compared the one used on
the web gotour.

Signed-off-by: Minux <72d850dbd8858b791995463d8539b5a379577f28@golang.org>

Go-zh/tour,Go-zh/tour,Go-zh/tour,Go-zh/tour