Auto merge of #2663 - woodruffw-forks:os-macos-style, r=JohnTitor
Auto merge of #2663 - woodruffw-forks:os-macos-style, r=JohnTitor

categories: "mac OS" -> "macOS"

This is a tiny nitpick that I noticed while opening #2662: Apple stylizes their operating system without the space, so I figured consistency with their style makes sense.

rust-lang/crates.io,rust-lang/crates.io,rust-lang/crates.io,rust-lang/crates.io