New formula: whois 5.0.20 [updated]

Since Insom has already made a pull request, but it's still not accepted.
https://github.com/Homebrew/homebrew-dupes/pull/53

However new version of whois has been released so I made a formula for new version of whois.

I'm so sorry if it's not following the rules but 
could you please check and accept my pull request.

Thanks,
Hiro