go-tour: update sub-repo import path
I missed the appengine one in last CL.

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/176670043
diff --git a/gotour/appengine.go b/gotour/appengine.go
index 0fdc19c..45a8394 100644
--- a/gotour/appengine.go
+++ b/gotour/appengine.go
@@ -15,7 +15,7 @@
 
 	"appengine"
 
-	_ "code.google.com/p/go.tools/playground"
+	_ "golang.org/x/tools/playground"
 )
 
 const runUrl = "http://golang.org/compile"