Adds default brew arm64 path

[tomcastleman]

This PR adds the default path for homebrew running on arm64 / Apple Silicon.

Presently launchd cannot locate the binary in the scheduled job.

[spencerwilson]

Thanks! While this is sufficient to fix #67 , a more permanent fix might be #63 , which would work no matter where Homebrew is installed (e.g., if its default install dir changes again in the future). It uses bin from here: https://docs.brew.sh/Formula-Cookbook#variables-for-directory-locations

[tomcastleman]

#63 is definitely the nicer / more portable solution if it works - I wasn't too familiar with homebrew variables.

This PR can be closed if the other one fixes the issue.

[mmrwoods]

Thanks for the PR, I have merged #63 as suggested to fix this issue, so will close this PR. Sorry it has taken so long to follow up on this.