#hash and Opal fixes

@YorickPeterse will update it even if I'm not really fond of using type to check if it works. 

For the record seems that all hashes are returned as `Fixnum` instead of integer. I'd see a better solution in storing the `#hash_class` somewhere and rewrite the expectation as `empty.hash.should be_kind_of(hash_class)` wdyt?