… in Lua >= 5.3

There were errors since Lua 5.3 in `test/cases/0230-tserialize-metatables.lua`:

```
Running test    test/cases/0230-tserialize-metatables.lua

Suite test      2
Metatable not ignored (i)
stack traceback:
        [C]: in function 'error'
        test/cases/0230-tserialize-metatables.lua:44: in function <test/cases/0230-tserialize-metatables.lua:44>
        [C]: in for iterator 'for iterator'
        lua-nucleo/tserialize.lua:167: in upvalue 'recursive_proceed_simple'
        lua-nucleo/tserialize.lua:300: in upvalue 'tserialize'
        test/test-lib/tserialize-test-utils.lua:16: in upvalue 'check_fn_ok'
        test/test-lib/tserialize-test-utils.lua:34: in upvalue 'check_ok'
        test/cases/0230-tserialize-metatables.lua:48: in field 'fn'
        lua-nucleo/suite.lua:177: in function <lua-nucleo/suite.lua:177>
        [C]: in function 'xpcall'
        lua-nucleo/suite.lua:177: in upvalue 'run'
        lua-nucleo/suite.lua:683: in function <lua-nucleo/suite.lua:679>
        [C]: in function 'xpcall'
        lua-nucleo/suite.lua:678: in upvalue 'run_test'
        lua-nucleo/suite.lua:729: in local 'run_tests'
        test/test.lua:171: in main chunk
        [C]: in ?
ERR
Suite test      3
Metatable not ignored (i)
stack traceback:
        [C]: in function 'error'
        test/cases/0230-tserialize-metatables.lua:56: in function <test/cases/0230-tserialize-metatables.lua:56>
        [C]: in for iterator 'for iterator'
        lua-nucleo/tserialize.lua:167: in upvalue 'recursive_proceed_simple'
        lua-nucleo/tserialize.lua:300: in upvalue 'tserialize'
        test/test-lib/tserialize-test-utils.lua:16: in upvalue 'check_fn_ok'
        test/test-lib/tserialize-test-utils.lua:34: in upvalue 'check_ok'
        test/cases/0230-tserialize-metatables.lua:60: in field 'fn'
        lua-nucleo/suite.lua:177: in function <lua-nucleo/suite.lua:177>
        [C]: in function 'xpcall'
        lua-nucleo/suite.lua:177: in upvalue 'run'
        lua-nucleo/suite.lua:683: in function <lua-nucleo/suite.lua:679>
        [C]: in function 'xpcall'
        lua-nucleo/suite.lua:678: in upvalue 'run_test'
        lua-nucleo/suite.lua:729: in local 'run_tests'
        test/test.lua:171: in main chunk
        [C]: in ?
```

The reason is that starting from Lua 5.3, size of the array tables with holes is
different that in older versions and is really undetermined as the Lua manual
always been said. This affects `ipair` iterators and broke
`tserialize.recursive_proceed_simple` when running the test.