message: Fix fontSize prop type
diff: @@ -41,7 +41,7 @@ Button.propTypes = {
  as: PropTypes.oneOfType([PropTypes.oneOf(['button', 'a', 'summary', 'input']), PropTypes.func]),
  children: PropTypes.node,
  disabled: PropTypes.bool,
  - fontSize: systemPropTypes.fontSize,
  + fontSize: systemPropTypes.typography.fontSize,
  onClick: PropTypes.func,
  theme: PropTypes.object,
  variant: PropTypes.oneOf(['small', 'medium', 'large']),
  