Travis pass does not check existence of `polymer.json`

[TimvdLippe]

The Travis pass currently adds linting to the script (https://github.com/PolymerLabs/tedium/blob/3684899d7ca344e84f4a1d7098ad794b36fe6ae4/cleanup-passes/travis.ts#L78-L83), however this will fail if polymer.json does not exist in the repository (which is the case for almost all elements).

The Travis pass (or maybe a different pass) should therefore generate a simple polymer.json with the correct linting configuration. Probably for the elements this should be

{
  "lint": {
      "rules": ["polymer-2-hybrid"]
  }
}