Update to NIST RDS 2.42 + drop IPv6 fetch

    Update of the URL to NIST RDS 2.40 and
    IPv4 is forced for wget and curl as the NIST website resolves
    in IPv6 but it's not reachable.
Merge pull request #4 from adulau/master

    Update to NIST RDS 2.42 + drop IPv6 fetch