Rename master branch to main
### Current Situation

As you might know, Git and GitHub introduced a new standard for master branch naming: 'main' And for consistency, I would like to see this change in the homebridge repo.

### Proposed Change

Rename master branch to 'main'.

### Additional Context

[https://github.blog/changelog/2020-10-01-the-default-branch-for-newly-created-repositories-is-now-main/](https://github.blog/changelog/2020-10-01-the-default-branch-for-newly-created-repositories-is-now-main/)
And some docs: [https://github.com/github/renaming/](https://github.com/github/renaming/)