fix: import performance explicitly

[danielroe]

🔗 Linked issue

❓ Type of change

• [ ] 📖 Documentation (updates to the documentation or readme)
• [x] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [ ] 👌 Enhancement (improving an existing functionality like performance)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Currently this module doesn't run on Node 14. The following error is thrown:

 ERROR  Could not build tokens!                                               design-tokens 15:40:33
 ERROR  performance is not defined                                            design-tokens 15:40:33

This PR resolves the issue by explicitly importing performance.

📝 Checklist

• [x] I have linked an issue or discussion.
• [ ] I have updated the documentation accordingly.

[netlify[bot]]

✅ Deploy Preview for nuxt-design-tokens ready!

Name	Link
🔨 Latest commit	80b6810646e1d257457d0a678af503379a726dd6
🔍 Latest deploy log	https://app.netlify.com/sites/nuxt-design-tokens/deploys/62e937acce0307000828a454
😎 Deploy Preview	https://deploy-preview-5--nuxt-design-tokens.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.