Detect upstream git branch based on git config

[ThisIsMissEm]

Currently, this tool hardcodes the usage of master as the upstream branch, which can often not be the case.

https://github.com/azz/pretty-quick/blob/master/src/scms/git.js#L31-L37

const revision = staged
      ? 'HEAD'
      : runGit(directory, [
          'merge-base',
          'HEAD',
          branch || 'master',
        ]).stdout.trim();

You can potentially provide better user experience by first checking if the user has configured a different default branch for their repos: git config --get init.defaultbranch, if that returns a value, then use that value, otherwise, use master (or if you wanna be progressive, main, but that'd be a breaking change — n.b., GitHub has published intent to change the default branch to always be main not master: https://github.com/github/renaming )

[JounQin]

Yes, it can be improved, currently you can use --branch option to override.