message: update Button to use is
diff: @@ -4,7 +4,7 @@ import PropTypes from 'prop-types'
  import {withSystemProps, COMMON} from './system-props'
  function Button({
  - tag: Tag = 'button',
  + is: Tag,
  children,
  size,
  block,
  @@ -36,6 +36,10 @@ function Button({
  )
  }
  +Button.defaultProps = {
  + is: 'button'
  +}
  +
  Button.propTypes = {
  block: PropTypes.bool,
  children: PropTypes.node,
  @@ -45,7 +49,7 @@ Button.propTypes = {
  onClick: PropTypes.func,
  scheme: PropTypes.string,
  size: PropTypes.oneOf(['sm', 'large']),
  - tag: PropTypes.oneOf(['button', 'a', 'summary'])
  + is: PropTypes.oneOf(['button', 'a', 'summary'])
  }
  export default withSystemProps(Button, COMMON)
  