Fix the Map for Option type

[tomohavvk]

After the first touch of Option type I was confused how the Map is implemented.

In my understanding of functional programming the Map should be applied only for a value and return the value, and never return the no-value.

For case when need to apply function for a value and return Some or None the FlatMap should be used.

Before:

Some(1).
  Map(func(value int) (int, bool) {
    return value + 21, true
  })

After:

Some(1).
  Map(func(value int) int {
    return value + 21
  })