style/build: rename default branch from master to main

[mannybecerra]

Request

As the PR title suggests, renaming the current default branch for swr-site from master to main.

• Made a suggestion in my recent PR here, doc: correcting a couple of typos in TypeScript section #204, however elevating it here as its own request so it can be properly reviewed/considered by the Vercel team. Please and thank you for the consideration.

Motivation

Adopt naming conventions that are more meaningful and inclusive.

Scope

• Current repository, swr-site, plus
• Any and all other repositories in the Vercel org scope that currently use master as the default branch name

Resources

• https://github.com/github/renaming

[shuding]

Thanks!