function reduce$1 (f, initial, stream) {
  return withDefaultScheduler(new Reduce(f, initial, stream.source))
}
Reduce a stream to produce a single result.  Note that reducing an infinite
stream will return a Promise that never fulfills, but that may reject if an error
occurs.
@param {function(result:*, x:*):*} f reducer function
@param {*} initial initial value
@param {Stream} stream to reduce
@returns {Promise} promise for the file result of the reduce