message: change file extension in index
diff: export {meta as Avatar} from './Avatar.md'
  export {meta as BorderBox} from './BorderBox.md'
  -export {meta as Box} from './Box.js'
  +export {meta as Box} from './Box.md'
  export {meta as BranchName} from './BranchName.md'
  export {meta as Buttons} from './Buttons.md'
  export {meta as CircleBadge} from './CircleBadge.md'
  