Update root zone hints, prompted by d.root-servers.net address change.

Data pulled from http://www.iana.org/domains/root/servers. (The new IPv4 address
for d.root-servers.net is based on the UMD announcement to the NANOG list; it
won't show up on the root servers or IANA lists for a couple of weeks, although
the server is now live at the new address.)