Inconsistent when hash has duplicate key.

### Example

  ```ruby
  # example.rb
  keys = (1..3).map{[_1]}
  h = keys.to_h{[_1, _1[0]]}
  keys[0][0] = 2
  p h.values
  p h.each_value.to_a
  p h
  ```

#### Before this patch:

  ```console
  $ bin/mruby example.rb
  [1, 2, 3]
  [1, 1, 3]
  {[2]=>1, [2]=>1, [3]=>3}
  ```

#### After this patch (same as Ruby)

  ```console
  $ bin/mruby example.rb
  [1, 2, 3]
  [1, 2, 3]
  {[2]=>1, [2]=>2, [3]=>3}
  ```