message: use typography system props in Heading
diff: -import React from 'react'
  -import Text from './Text'
  +import system from 'system-components/emotion'
  +import {TYPOGRAPHY} from './system-props'
  -const Heading = props => <Text {...props} />
  +const Heading = system(...TYPOGRAPHY)
  -Heading.defaultProps = {
  - tag: 'h1',
  +Object.assign(Heading.defaultProps, {
  + is: 'h1',
  fontSize: 5,
  m: 0
  -}
  -
  -Heading.propTypes = {
  - ...Text.propTypes
  -}
  +})
  export default Heading
  