[tz] Secure FTP support for IANA downloads

[Kim Davies]

Quoting pbassey--- via tz on Tuesday June 05, 2018:
>
> Hello, I am writing to inquire about your site's use of FTP and the
> possibility of migrating over to Secure FTP in order to comply with
> our company's security compliance requirements.
>
> Does your site offer Secure FTP for your IANA downloads and if not,
> what would it take to enable this protocol so our company could
> securely download your files? Currently, we use this URL to download
> the IANA time zone files which is not secure: ftp://ftp.iana.org/tz/

We don't currently have any plans to offer Secure FTP, but as others
have noted, there are other secure options, as well as alternate ways to
verify authenticity through FTP.

Here are some secure URLs to get you started:

    https://data.iana.org/time-zones/tzcode-latest.tar.gz
    https://data.iana.org/time-zones/tzdata-latest.tar.gz
    https://data.iana.org/time-zones/tzdb-latest.tar.lz

kim