message: add m + p utils to UnderlineNavLink
diff: @@ -5,8 +5,7 @@ import {ITEM_CLASS, SELECTED_CLASS} from './UnderlineNav'
  import {mapWhitespaceProps} from './props'
  export default function UnderlineNavLink(props) {
  - const {children, selected, tag: Tag, ...rest} = props
  - const {className} = mapWhitespaceProps(rest)
  + const {children, selected, tag: Tag, className, ...rest} = mapWhitespaceProps(props)
  const classes = classnames(ITEM_CLASS, selected && SELECTED_CLASS, className)
  return (
  