values() {
    throw new Error('Not implemented');
  }
The values() method returns a new Iterator object that
contains the values for each element in the Map object
in insertion order.

@example
  const myMap = new HashMap();
  myMap.set('0', 'foo');
  myMap.set(1, 'bar');
  myMap.set({}, 'baz');

  var mapIter = myMap.values();

  console.log(mapIter.next().value); // "foo"
  console.log(mapIter.next().value); // "bar"
  console.log(mapIter.next().value); // "baz"