chore: use "main" for main branch name

use "main" for main branch name

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)
[ ] I have read the CONTRIBUTING document
[ ] My code follows the code style of this project (hint: install an xo editor plugin)
[ ] Any required documentation has been added
[ ] I have added tests to cover my changes