Renamed bbolt master to main

[Benjamin Wang]

Hello,

I just renamed bbolt's master branch to main. All the existing PRs were automatically closed. Please feel free to raise a new PR against the new main branch if you want. I will also evaluate all the closed PRs, and resurrect them if it's needed and the original authors do not have time to do it. Sorry for the inconvenience. 

If you have a local clone, please execute the following commands,

$ git branch -m master main
$ git fetch origin
$ git branch -u origin/main main
$ git remote set-head origin -a

Regards,

Benjamin