PSA: this repo has been moved to the main babel repo

[hzoo]

Now that babel-preset-env has stabilized, it has been moved into the main Babel mono-repo.

The move makes it much easier to release and develop in sync with the rest of Babel!

This repo will be made read-only, as all of the issues/labels have been moved over as well. Please report any bugs and open pull requests over on the main mono-repo.