Browser-compat-data: Rename default branch

[ddbeck]

We ought to abandon the name master for our default branch, given its origins. We try to make new contributors feel welcome to BCD, including first-time FOSS contributors who may be surprised or discouraged by the conventional default branch name. It may be a small thing, but breaking from convention in this case would be consistent with that effort.

I propose we switch to something less fraught and potentially more descriptive, such as main or trunk.

The process of renaming the branch itself isn't too complicated. However, we would need to investigate any changes we'd need to make to reflect the name change. For example, we have a few references to the default branch name in our documentation and many links point to the default branch by name.

Tasks

• [ ] Choose a new default branch name
• [ ] Come up with and carry out a process to warn committers
• [ ] Rewrite documentation links

[Elchi3]

I agree to do this. https://github.com/github/renaming/ has useful information about what happens on the GitHub side. "Later this year: seamless move for existing repositories" seems promising and is the reason we haven't been actively working on this so far.

[Elchi3]

Some more details available here now: https://github.com/github/renaming#creating-a-seamless-move-for-existing-repositories-

[saschanaz]

The feature is now landed: https://github.com/github/renaming#renaming-existing-branches