gettor - Create alias "macos"

We got this feedback:

It seems that the instruction (https://support.torproject.org/censorship/gettor-2/) lists the macOS as macOS, while the email service requires "osx" string to be present for the valid instructions to be returned.

Consider making an alias from "macos" to "osx" so that the users won't be confused.

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If that is not possible, I will fix the main support documentation.