The resource is available over (and redirects to) HTTPS, it seems like a good
idea to save a redirect and ensure an encrypted connection.

Change-Id: I262c7616ae289cdd756b6f67573ba6bd7e3e0ca6
Reviewed-on: https://go-review.googlesource.com/23104Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>