Add support for updating multiple nameservers via dns_nsupdate

[marshallwp]

The dnsapi/dns_nsupdate.sh dnsapi script is used for DNS-01 acme challenges. However it currently only supports updating a single nameserver during such challenges. In the event your network admin requires you to update multiple nameservers during such challenges, the current script does not work.

Fixing this is relatively simple: change NSUPDATE_SERVER to a space-delimited list of servers instead of a single server and then loop through them during the challenge.

I will be making a pull request to solve this just as soon as I can get through all the setup for that.

EDIT: This will take longer than expected. I wasn't initially aware that tests would include actual usage. I don't currently have a way to test DNS-01 challenges remotely; the DNS servers I have access to do not accept changes from the internet.

[github-actions]

Please upgrade to the latest code and try again first. Maybe it's already fixed. acme.sh --upgrade If it's still not working, please provide the log with --debug 2, otherwise, nobody can help you.