Add dataset/mlsum
CONTRIBUTOR
I think the problem is related to `wiki_dpr` dataset which is making the circle CI failed as you can see:
```
FAILED tests/test_dataset_common.py::AWSDatasetTest::test_load_dataset_wiki_dpr
FAILED tests/test_hf_gcp.py::TestDatasetOnHfGcp::test_script_synced_with_s3_wiki_dpr/dummy_psgs_w100_no_embeddings
FAILED tests/test_hf_gcp.py::TestDatasetOnHfGcp::test_script_synced_with_s3_wiki_dpr/dummy_psgs_w100_with_nq_embeddings
FAILED tests/test_hf_gcp.py::TestDatasetOnHfGcp::test_script_synced_with_s3_wiki_dpr/psgs_w100_no_embeddings
FAILED tests/test_hf_gcp.py::TestDatasetOnHfGcp::test_script_synced_with_s3_wiki_dpr/psgs_w100_with_nq_embeddings

```
I'm facing the same issues with my last commits, I tried to rebase from master but it still not working. Maybe @lhoestq can help with.
2020-08-03T08:26:13Z
https://github.com/huggingface/datasets/pull/463#issuecomment-667884794
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2020-08-03T08:26:13Z
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CONTRIBUTOR
Hello, I am confused about the next steps I need to do. Did the forced merge solve the issue ?
2020-08-24T13:02:03Z
https://github.com/huggingface/datasets/pull/463#issuecomment-679112333
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2020-08-24T13:02:03Z
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MEMBER
Hello :)
I think you can just rebase from master and it should solve the CI error
2020-08-24T13:23:45Z
https://github.com/huggingface/datasets/pull/463#issuecomment-679123634
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2020-08-24T13:23:45Z
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New pull request that should correct the previous errors. 

The load_real_data stills fails because it is looking for a default dataset URL that does not exists, this does not happen when loading the dataset with load_dataset