message: rewrite Heading as vanilla JSX
diff: import React from 'react'
  import Text from './Text'
  -const Heading = Text.withComponent('h1', true)
  +const Heading = props => <Text {...props} />
  Heading.defaultProps = {
  + tag: 'h1',
  fontSize: 5,
  m: 0
  }
  +Heading.propTypes = {
  + ...Text.propTypes
  +}
  +
  export default Heading
  