Not compatible with spacy 3.x

When running the sample code I get the following error:

```
---------------------------------------------------------------------------
ModuleNotFoundError Traceback (most recent call last)
in
1 import doccano_transformer
2
----> 3 from doccano_transformer.datasets import NERDataset
4 from doccano_transformer.utils import read_jsonl
5

~/miniconda3/envs/base/lib/python3.7/site-packages/doccano_transformer/datasets.py in
3 from typing import Any, Callable, Iterable, Iterator, List, Optional, TextIO
4
----> 5 from doccano_transformer.examples import Example, NERExample
6
7

~/miniconda3/envs/base/lib/python3.7/site-packages/doccano_transformer/examples.py in
2 from typing import Callable, Iterator, List, Optional
3
----> 4 from spacy.gold import biluo_tags_from_offsets
5
6 from doccano_transformer import utils

ModuleNotFoundError: No module named 'spacy.gold'
```

Seems like this is removed from spacy v3.x: https://github.com/explosion/spaCy/releases