code: function repoFiles (options, callback) {
    var url = options.url
    var files = options.files
  
    if (!url || !files) {
      return callback(new Error('must specify url, files'))
    }
  
    var data = []
  
    async.forEachOf(files, function (item, key, callback) {
      request({
        url: url + item.name
      }, function (err, json) {
        if (err) return callback(err)
  
        if (json && json.type && json.type === 'FeatureCollection') {
          json.name = item.name
          json.sha = item.sha
          data.push(json)
  
          return callback(null)
        }
  
        callback(new Error('problem accessing file ' + url + '/' + key))
      })
    }, function (err) {
      if (err) return callback(err)
      callback(null, data)
    })
  }
docs: get geojson files from a specific raw.github.com repo directory URL
  
  @private
  @param  {object}   options - url, files
  @param  {Function} callback - err, data