tour: fix for new app deployment

The app now runs in the root of the repo, so need to use "tour" not "." for tour root.

Fixes golang/go#46793.

Change-Id: I14499e0c662793789bc1a2603db9dd7c0e1011ad
Reviewed-on: https://go-review.googlesource.com/c/website/+/328675
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Website-Publish: Russ Cox <rsc@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

tour/appengine.go

@@ -21,14 +21,16 @@ func gaeMain() {
 	socketAddr = gaeSocketAddr
 	analyticsHTML = template.HTML(os.Getenv("TOUR_ANALYTICS"))
 
-	if err := initTour(".", "HTTPTransport"); err != nil {
+	root := "tour"
+
+	if err := initTour(root, "HTTPTransport"); err != nil {
 		log.Fatal(err)
 	}
 
 	http.Handle("/", hstsHandler(rootHandler))
 	http.Handle("/lesson/", hstsHandler(lessonHandler))
 
-	registerStatic(".")
+	registerStatic(root)
 
 	port := os.Getenv("PORT")
 	if port == "" {