Fix typo in gradio-tools docs
Author: freddyaboulton
Pull request: yes

# What does this PR do?
Fixes a typo in the gradio-tools guide, `tool` vs `tools`, that prevents the code snippet from running.

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## Before submitting
- [x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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- [ ] Did you write any new necessary tests?


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Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_23305). All of your documentation changes will be reflected on that endpoint.