function flattenForever (array, result) {
  for (var i = 0; i < array.length; i++) {
    var value = array[i];

    if (Array.isArray(value)) {
      flattenForever(value, result);
    } else {
      result.push(value);
    }
  }

  return result
}
Set an object of headers on a response.

@param {object} res
@param {object} headers
@private