iana.org, www.iana.org and data.iana.org all present a valid TLS
certificate, so let's use it when fetching data or linking to
resources to avoid errors in transit.

Change-Id: Ib3ce7c19789c4e9d982a776b61d8380ddc63194d
Reviewed-on: https://go-review.googlesource.com/89416Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>