gotour: redirect from HTTP to HTTPS on App Engine

Change-Id: I3e0c825d8a6d1cf41ab87f337943cb042f70a308
Reviewed-on: https://go-review.googlesource.com/22362
Reviewed-by: Francesc Campoy Flores <campoy@golang.org>
diff --git a/app.yaml b/app.yaml
index c602929..dfff2d5 100644
--- a/app.yaml
+++ b/app.yaml
@@ -11,13 +11,17 @@
 - url: /favicon.ico
   static_files: static/img/favicon.ico
   upload: static/img/favicon.ico
+  secure: always
 - url: /content/img
   static_dir: content/img
+  secure: always
 - url: /static
   static_dir: static
   application_readable: true
+  secure: always
 
 - url: /(.*|list|lesson/.*|compile|fmt|script\.js)
   script: _go_app
+  secure: always
 
 nobuild_files: (solutions|content)/.*