new formula: nikto

Let's give it one more try - this is a formula taken from old pull request that was never merged due to inactivity from the author - https://github.com/Homebrew/homebrew/pull/28537

I've fixed small things that were asked in the comments to the original PR 
I am not entirely sure how to fix it in upstream - nikto is a perl application, no build steps are involved. The recommended approach seems to be to download release tarball, unpack it and either replace hard-coded value /etc/nikto.conf (as documented in the source code - see https://github.com/sullo/nikto/blob/master/program/nikto.pl#L48) or always use --config command line option (see https://github.com/sullo/nikto/blob/master/program/nikto.pl#L231)