Update requirements.txt for text_to_image

[ktakita1011]

I tried examples/text_to_image/train_text_to_image.py but it did not work because the version of the datasets library is out of date. If the datasets library is old, it will not read the metadata.jsonl and the label will default to an integer of type int.

It worked by setting the version of the datasets library to 2.19 or higher.

[sayakpaul]

Cc: @lhoestq

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[yiyixuxu]

@sayakpaul can we merge this now?