Fix loading json in tutorial_datdaset.py

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Hi
Thanks for your great repo.

Here is how to save the json
```python
with open(prompt_json_path, "w") as prompt_file:
json.dump(prompt_data, prompt_file)
```

Here is how to load it
```python
with open(prompt_json_path, "r") as prompt_file:
data = json.loads(prompt_file.read())
```

How its done on tutorial_dataset.py is:
```python
with open(json_file, 'rt') as f:
for line in f:
self.data.append(json.loads(line))

```

Please fix this.

Thanks

Read tutorial_dataset.py and compare its JSON loading with the save and load examples in the issue. Align the loader with the JSON format used by the tutorial, then verify that the tutorial dataset loads successfully without parsing errors.

Written by the indexing model from the issue text.