Installation of mac brew vim version 8.1
There is a pull request on homebrew's github to update the Vim formula to 8.1: https://github.com/Homebrew/homebrew-core/pull/27983

When that merges, just run brew upgrade vim.

If you want to install 8.1 yourself, you can do so by cloning and following the build instructions on the vim official repo: https://github.com/vim/vim.