Set to_json default to JSON lines
CONTRIBUTOR
This is perfect, @albertvillanova - thank you! Tested it to work.

Might it be a good idea to document the args to `to_json`?

and also even a very basic progress bar? took 10min for 8M large records for `openwebtext` so perhaps some indication of it's being alive every min or so?
2021-05-12T18:35:09Z
https://github.com/huggingface/datasets/pull/2352#issuecomment-840009285
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2021-05-12T19:05:35Z
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@lhoestq I added tests for both `lines` and `orient`.
2021-05-21T06:28:28Z
https://github.com/huggingface/datasets/pull/2352#issuecomment-845691929
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With this PR, the method `Dataset.to_json`:
- is added to the docs
- defaults to JSON lines