Fix some Hash methods are inconsistent with values

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}
  ```

mrblib/hash.rb

@@ -140,7 +140,7 @@ def each_key(&block)
   def each_value(&block)
     return to_enum :each_value unless block
 
-    self.keys.each{|k| block.call(self[k])}
+    self.values.each{|v| block.call(v)}
     self
   end
 
@@ -192,11 +192,11 @@ def _inspect(recur_list)
     recur_list[self.object_id] = true
     ary=[]
     keys=self.keys
+    vals=self.values
     size=keys.size
     i=0
     while i<size
-      k=keys[i]
-      ary<<(k._inspect(recur_list) + "=>" + self[k]._inspect(recur_list))
+      ary<<(keys[i]._inspect(recur_list) + "=>" + vals[i]._inspect(recur_list))
       i+=1
     end
     "{"+ary.join(", ")+"}"