message: add whitespace (margin + padding) props to OcticonButton
diff: import React from 'react'
  import PropTypes from 'prop-types'
  +import classnames from 'classnames'
  import Octicon from '@github/octicons-react'
  +import {mapWhitespaceProps} from './props'
  -export default function OcticonButton({disabled, icon, label, onClick, size}) {
  - const buttonProps = {'aria-label': label, disabled, onClick}
  +export default function OcticonButton({disabled, icon, label, onClick, size, ...rest}) {
  + const {className} = mapWhitespaceProps(rest)
  + const buttonProps = {
  + 'aria-label': label,
  + className: classnames('btn-link text-inherit', className),
  + disabled,
  + onClick
  + }
  const octiconProps = {icon, size}
  return <button {...buttonProps}><Octicon {...octiconProps} /></button>
  }
  