talks: redirect HTTP traffic to HTTPS

Set secure to always on all handlers so that HTTP traffic
is redirected to an HTTPS URL with the same path.

References:

•	https://cloud.google.com/appengine/docs/standard/go/application-security#https_requestshttps://cloud.google.com/appengine/docs/standard/go/config/appref#handlers_secure

For golang/go#42281.

Change-Id: Id89fbcfe97df255173e87f0af4ec71f5238897dc
Reviewed-on: https://go-review.googlesource.com/c/talks/+/266837
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Alexander Rakoczy <alex@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
diff --git a/app.yaml b/app.yaml
index 464e028..ed889e7 100644
--- a/app.yaml
+++ b/app.yaml
@@ -8,9 +8,12 @@
 - url: /favicon.ico
   static_files: static/favicon.ico
   upload: static/favicon.ico
+  secure: always
 - url: /static
   static_dir: static
+  secure: always
 - url: /.*
   script: auto
+  secure: always
 
 nobuild_files: content/