message: spread Box.defaultProps into CaretBox
diff: import React from 'react'
  +import Box from './Box'
  import {Position} from './Position'
  import Caret from './Caret'
  @@ -22,11 +23,7 @@ CaretBox.propTypes = {
  CaretBox.defaultProps = {
  ...Position.defaultProps,
  - // FIXME: spread Box.defaultProps here?
  - bg: 'white',
  - border: 1,
  - borderColor: 'gray.2',
  - borderRadius: 1,
  + ...Box.defaultProps,
  position: 'relative'
  }
  