Bug in tokenizer for Tibetian Language

At the moment you cant use tibetian language tokenizer. It gives the error message:

`TypeError: "module" object is not callable`

The error is thrown here in sentence_split.py:
```
    elif split_algo == "bodnlp":
        logger.info(f" - Tibetan NLTK sentence splitter applied to '{lang}'")
        from botok.tokenizers import sentencetokenizer as bod_sent_tok
```