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 
What happens if you don't do this? Is this Homebrew-specific? Does it write files in `$HOME` (if not we can/should run it for the user).