go-tour: use moved playground package

Fixes  issue 104 .

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/11977043
diff --git a/gotour/appengine.go b/gotour/appengine.go
index 343ca8d..bb23643 100644
--- a/gotour/appengine.go
+++ b/gotour/appengine.go
@@ -14,7 +14,7 @@
 
 	"appengine"
 
-	_ "code.google.com/p/go.talks/pkg/playground"
+	_ "code.google.com/p/go.tools/godoc/playground"
 )
 
 const runUrl = "http://golang.org/compile"