fix headers option in next.config.js

[chenxsan]

Noticed this error in console when running yarn dev:

If we inspect the response header at https://swap.defillama.com/, you can find they weren't added:

Hence I've updated the config accordingly per https://nextjs.org/docs/api-reference/next.config.js/headers.

[vercel[bot]]

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Name	Status	Preview	Comments	Updated
llamaswap	✅ Ready (Inspect)	Visit Preview	💬 Add your feedback	Jan 28, 2023 at 7:38AM (UTC)

[chenxsan]

And here's the response headers from the preview url:

[chenxsan]

Oops, seems something's wrong when deploying production to vercel.

[mintdart]

its not related to ur PR, something wrong with fetching token lists