Original:

{ hk1 => 5, hk2 => [[1, 2, 3], [4, 5, 8]] }

The new dump string:

{
  "hk1" => 5,
  "hk2" =>
    [
      [ 1, 2, 3 ],
      [ 4, 5, 8 ]
    ]
}

Validation of the new dump:

{ hk1 => 5, hk2 => [[1, 2, 3], [4, 5, 8]] }

 VALID :)