Add wiki40b
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Looks good to me. I have not really looked too much into the Beam Datasets yet though - so I think you can merge whenever you think is good for Beam datasets :-) 
2020-05-13T12:30:35Z
https://github.com/huggingface/datasets/pull/88#issuecomment-627950253
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2020-05-13T12:30:35Z
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This one is a beam dataset that downloads files using tensorflow.
I tested it on a small config and it works fine