message: Use built-in fontSize system
diff: @@ -3,7 +3,7 @@ import styled from 'styled-components'
  import {COMMON, get} from './constants'
  import theme from './theme'
  import buttonStyles from './ButtonStyles'
  -import {compose, system, layout} from 'styled-system'
  +import {compose, layout, fontSize} from 'styled-system'
  import systemPropTypes from '@styled-system/prop-types'
  const fontSizeVariants = {
  @@ -23,13 +23,7 @@ const Button = styled.button.attrs(({disabled, onClick}) => ({
  ${buttonStyles}
  ${variants}
  ${compose(
  - system({
  - fontSize: {
  - property: 'fontSize',
  - cssProperty: 'fontSize',
  - scale: 'fontSizes'
  - }
  - }),
  + fontSize,
  COMMON,
  layout
  )}
  @@ -45,7 +39,7 @@ Button.propTypes = {
  as: PropTypes.oneOfType([PropTypes.oneOf(['button', 'a', 'summary', 'input']), PropTypes.func]),
  children: PropTypes.node,
  disabled: PropTypes.bool,
  - fontSize: PropTypes.number,
  + fontSize: systemPropTypes.fontSize,
  onClick: PropTypes.func,
  theme: PropTypes.object,
  variant: PropTypes.oneOf(['small', 'medium', 'large']),
  