Fix subtitle for some package results

[patrik-csak]

This fixes a bug I discovered while searching for consola.

One of the search results is the @types/consola package which is missing date, author, and publisher.

GET https://api.npms.io/v2/search?q=%40types%2Fconsola

{
  "total": 1,
  "results": [
    {
      "package": {
        "name": "@types/consola",
        "version": "0.0.0",
        "links": {
          "npm": "https://www.npmjs.com/package/%40types%2Fconsola"
        }
      },
      "score": {
        "final": 0,
        "detail": {
          "quality": 0,
          "popularity": 0,
          "maintenance": 0
        }
      },
      "searchScore": 100000
    }
  ]
}

I also included a commit which fixes the existing test.

[sindresorhus]

You're right, we should not assume package.author exists, but package.date should exist and is a bug: npms-io/npms-api#82