message: add CounterLabel.propTypes
diff: import React from 'react'
  +import PropTypes from 'prop-types'
  import classnames from 'classnames'
  const CounterLabel = ({theme, children}) => (
  <span className={classnames('Counter', theme ? `Counter--${theme}` : null)}>{children}</span>
  )
  +CounterLabel.propTypes = {
  + children: PropTypes.node,
  + theme: PropTypes.oneOf(['gray', 'gray-light'])
  +}
  +
  export default CounterLabel
  