openfst version

Hi,

Which version of openfst is this compatible with? symb_map\[\<other>\] in [expand_other_symbols](https://github.com/dmort27/fststr/blob/3bacf42c22dc2e6261ca21a26fa78a135ceed9d6/fststr/fststr.py#L114) throws keyerror as symbols in FST are byte encoded rather than plain strings.