[x/tour] tour: update Spanish tour link
[x/tour] tour: update Spanish tour link

Currently, go-tour-es.appspot.com is a 404, but the correct link
for Spanish tutorial can be seen at gotour-es.appspot.com.

Change-Id: I3e3f34a6e72fb59283c8a282b5e996babdf1e9f3
GitHub-Last-Rev: ce817cb3e1d7f4b1a30c9f0f43f5abed5555affc
GitHub-Pull-Request: golang/tour#687
Reviewed-on: https://go-review.googlesource.com/c/158918
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>
X-Tour-Commit: 838ce51196a7e9f9bff83402caf4f678dc0f0d75

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website