Add minimum OS versions to stop warnings

[CraigsOverItAll]

• with a podspec.json if a platform version isn’t defined, the lowest version available will be used.
• ’os_unfair_lock_trylock' is only available on iOS 10.0, macOS 10.12, tvOS 10.0 and watchOS 3.0 or newer
• see Apple Docs

Thanks for wanting to contribute to this project!

Unfortunately, it's not really maintained anymore.

Feel free to use it as-is, or fork it and modify as much as you want to suit your needs. However, I can't guarantee that I'll have time/energy to look at new issues and pull requests.

Sorry for the trouble!