feat: update create-next-app to init with main as initial branch (#17745)
feat: update create-next-app to init with main as initial branch (#17745)

When `create-next-app` is initialized a git repo, it now uses 'main' as the initial branch.

The branch master does not actually exist initially. The branches don't get created only when they have at least one commit. Until the branch gets created, the branch only exists in .git/HEAD. So there is no master branch initialized in the repo.

Closes: https://github.com/vercel/next.js/issues/17733

<img width="639" alt="Screenshot 2020-10-09 at 17 26 30" src="https://user-images.githubusercontent.com/4656109/95580229-9f3c6c80-0a54-11eb-967f-180eb9601c1a.png">

azukaru/next.js,JeromeFitz/next.js,flybayer/next.js,JeromeFitz/next.js,flybayer/next.js,JeromeFitz/next.js,flybayer/next.js,JeromeFitz/next.js,azukaru/next.js,flybayer/next.js,zeit/next.js,zeit/next.js,azukaru/next.js,azukaru/next.js,zeit/next.js