function performSave(step, task, results) {
  var db = mongoose.connection.db;

  return step.useMongoose
    ? goose.performSave(step, task, results)
    : native.nativeSave(db, step, task, results)
}
This function handles the save step.

@param step the save step
@param task the task which step belongs to
@param results array of results from previous operations

@returns {Promise|*}