Rename `master` -> `main` for llvmlite

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Dear *,

I will rename the default branch for llvmlite from master to main today (now).

Please follow the ticket at: Rename `master` to `main`. · Issue #814 · numba/llvmlite · GitHub and post any issues this may cause there too.

Thank you for your patience!

V-

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these instructions were provided by GitHub for our community members!

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This is now done, thank you!