Minor fix in itty-router.md

[andre-j3sus]

[github-actions[bot]]

🧪 A prerelease is available for testing 🧪

You can install this latest build in your project with:

npm install --save https://prerelease-registry.devprod.cloudflare.dev/chanfana/runs/11023127012/npm-package-itty-router-openapi-177

Or you can immediately run this with npx:

npx https://prerelease-registry.devprod.cloudflare.dev/chanfana/runs/11023127012/npm-package-itty-router-openapi-177