symbolize_keys is silently swallowed by BSON::OrderedHash

I needed to use some hash methods, like `symbolize_keys` but it doesn't work, nothing happens ; keys are not symbolized, no error is raised, ...

Maybe I'm doing something wrong, but this doesn't seem right to me.

If it's expected that symbolize_keys not to work, an error should be raised.

If it's a bug, then I'd be happy to try and help to solve it.