4.0.0

Change

• f196da2 Update @types/hast, utilities
  migrate: update too
• ad8812e Change to require Node.js 16
  migrate: update too
• 1581905 Change to use exports
  migrate: don’t use private APIs
• 21810d7 Change to yield undefined
  migrate: expect undefined, keep a reference to the passed tree

Full Changelog: 3.0.1...4.0.0