6.0.0

Change

• ed58cd9 Update @types/mdast
  migrate: update too
• 13bdeab Change to require Node.js 16
  migrate: update too
• b12a1b9 Change to use export map
  migrate: don’t use private APIs
• 7a4a5e1 Change to return undefined
  migrate: expect undefined

Fix

• c332c07 Fix package name in docs
  by @SaekiTominaga in #2

Full Changelog: 5.2.1...6.0.0