message: add m & p utility props to BranchName
diff: import React from 'react'
  import PropTypes from 'prop-types'
  +import classnames from 'classnames'
  +import {mapWhitespaceProps} from './props'
  -export default function BranchName({children, href, tag: Tag}) {
  +export default function BranchName(props) {
  + let {children, href, tag: Tag, className} = mapWhitespaceProps(props)
  // We don't want someone to use href on a non tag
  if (Tag !== 'a') {
  href = null
  }
  return (
  - <Tag href={href} className="branch-name">
  + <Tag href={href} className={classnames('branch-name', className)}>
  {children}
  </Tag>
  )
  