code: function renameKey (name, opts) {
    if (opts && opts.renameKey) {
      return opts.renameKey(name, opts)
    }
    return name
  }
docs: Default `renameKey` function. Pass a custom function to
  `opts.renameKey` to override.
  
  @param  {String} `name`
  @param  {Object} `opts`
  @return {String}