Handle rename of primary branch from "master" to "main"

[jmurty]

References on renaming primary branch in GitHub and Git:

• https://github.com/github/renaming#rename-existing
• https://docs.github.com/en/github/administering-a-repository/renaming-a-branch#updating-a-local-clone-after-a-branch-name-changes

[jmurty]

@elasticdog Let's do this branch rename to "main"

I don't have access to settings on this repository, but you should be able to change the default branch at https://github.com/elasticdog/transcrypt/settings/branches

See also the useful references in this PR's description (and the commit message)