Fix description of streaming in the docs
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2022-11-29T18:06:19Z
https://github.com/huggingface/datasets/pull/5313#issuecomment-1331086203
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2022-12-01T14:03:16Z
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We say that "the data is being downloaded progressively" which is not true, it's just streamed, so I fixed it. Probably I missed some other places where it is written? 

Also changed docstrings for `StreamingDownloadManager`'s `download` and `extract` to reflect the same, as these docstrings are displayed in the documentation cc @lhoestq 