async functions require extra time with `nuxt generate`

🐛 The bug When generated files are produced, async functions or serverPrefetches don't correctly populate the Nuxt context.

Note: I believe this is an issue with Nuxt rather than with nuxt-composition-api.

🛠️ To reproduce Steps to reproduce the behavior:

1. Clone this repo.
2. Remove interval: 2000 from test/fixture/nuxt.config.js
3. Run yarn nuxt generate -c test/fixture/nuxt.config.js
4. Inspect ./dist/ssr-ref/index.html to see not all ssrRefs injected in page

ℹ️ Workaround You can add time between pages being generated to allow for any async functions to resolve, if you are pre-generating any of your pages.

nuxt.config.js:

{
  generate: {
    // choose to suit your project
    interval: 2000,
  }
}