message: tidy up Label, add propTypes
diff: import React from 'react'
  +import PropTypes from 'prop-types'
  import classnames from 'classnames'
  const colorScheme = (scheme, outline) => {
  @@ -16,13 +17,15 @@ const colorScheme = (scheme, outline) => {
  }
  }
  -const Label = props => {
  +export default function Label(props) {
  const {outline, scheme, children} = props
  return (
  - <span className={classnames('Label', outline ? 'Label--outline' : '', colorScheme(scheme, outline))}>
  - {children}
  - </span>
  + <span className={classnames('Label', outline && 'Label--outline', colorScheme(scheme, outline))}>{children}</span>
  )
  }
  -export default Label
  +Label.propTypes = {
  + children: PropTypes.node,
  + outline: PropTypes.bool,
  + scheme: PropTypes.oneOf(['gray', 'gray-darker', 'green', 'orange'])
  +}
  