Use main as the default branch

[dbeatty10]

Background

The default branch for https://github.com/dbt-labs/hub.getdbt.com is currently master. It is hard-coded within Python in a place or two within this repo (https://github.com/dbt-labs/hubcap). Use git grep "master" ./ to discover those locations. It is unknown if this branch name is also specified within Netlify.

Next steps

1. Discover if the branch name is hard-coded within Netlify configuration -- update the following steps depending on the discoveries
2. Copy master to main within https://github.com/dbt-labs/hub.getdbt.com
3. Update hubcap to point to main branch
4. Redploy hubcap
5. Drop master branch in hub.getdbt.com