Starting on or about the 2018c archives, www.iana.org is redirected to
data.iana.org.  Tell curl to follow the redirect.

Updates: #22487

Change-Id: I00acada1a3ba01ef701d6d4ffae6cc2cbb6a068f
Reviewed-on: https://go-review.googlesource.com/89375Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>