Fix 'unix' brand letter casing

[hsnabszhdn]

Yet another PR similar to #615

The trademark is registered as "UNIX®", but when referred as a generic name (to refer to the broader family of Linux, FreeBSD, OpenBSD, etc.), it's usually written as "Unix".

Unix - Wikipedia

⚖️ Disclaimer: I'm not a lawyer and it's not a legal advice. I'm just an engineer talking based on what I've seen/read around the Internet. It's up to the core maintainers to consider proper use and permissions of all trademarks. I take no responsibility for copyright infringements, trademark usage violations, or any financial/collateral damage (if any).