Rename custom tap from mas-cli/tap to mas-cli/mas

[rgoldberg]

The custom tap should be renamed as mas-cli/mas instead of the current mas-cli/tap, which requires renaming its repo from homebrew-tap to homebrew-mas.

We would want to make an alias from mas-cli/tap to mas-cli/mas (or just have 2 equivalent taps), hopefully with automatic switch from mas-cli/mas to mas-cli/tap, or at least some warning outputs to tell people to manually switch.

All the documentation would tell people to use the correctly named tap.