3.0.0

Change

• 4cccf07 Update @types/mdast
  migrate: update too
• 9a8b284 Change to require Node.js 16
  migrate: update too
• 716dd61 Change to use export map
  migrate: don’t use private APIs
• 60c4a49 Change to return undefined, not null
  migrate: expect `undefined

Full Changelog: 2.0.1...3.0.0