The only change compared to 4.0.0-beta.1 is fixing peerDependencies so that jQuery Migrate 4.0.0-beta.2 can be installed alongside jQuery 4.0.0-beta.2 or newer. 4.0.0-beta.1 required a stable jQuery 4.0.0 or newer which doesn't exist yet.
Read the 4.0.0-beta.1 release notes for more details.