Modify macOS name in docs/faq.md

[JackLau1222]

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macOS hasn't been called "Mac OS" for a while

macOS is a more modern name, mac OS usually refers to Classic Mac OS which is the series of operating systems developed for the Macintosh family of personal computers by Apple Computer, Inc. from 1984 to 2001, starting with System 1 and ending with Mac OS 9. you can find more details at this link