https://medium.com/@remarkablemark/how-to-deploy-a-parcel-build-to-heroku-fa1ea74d2b96

serve.json

{
  "public": "dist",
  "rewrites": [{ "source": "**", "destination": "/index.html" }],
  "headers": [
    {
      "source": "**",
      "headers": [
        {
          "key": "Cache-Control",
          "value": "public, max-age=0, must-revalidate"
        }
      ]
    },
    {
      "source": "**/*.@(css|ico|jpg|jpeg|js|gif|png)",
      "headers": [
        {
          "key": "Cache-Control",
          "value": "public, max-age=31536000, immutable"
        }
      ]
    }
  ]
}