Fix text-classification tags
MEMBER
LGTM, thanks for fixing.
2021-03-15T08:34:12Z
https://github.com/huggingface/datasets/pull/2049#issuecomment-799225236
https://api.github.com/repos/huggingface/datasets/issues/2049
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2021-03-15T08:34:12Z
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There are different tags for text classification right now: `text-classification` and `text_classification`:
![image](https://user-images.githubusercontent.com/29076344/111042457-856bdf00-8463-11eb-93c9-50a30106a1a1.png).

This PR fixes it.
