[key: number] implementation is incorrectly open-ended, like [key: string]

[Logopher]

I have a type like this:

export type List<T> = { [index: number]: T };

The generator writes it like this (for List):

{
  "additionalProperties": {
    "$ref": "#/definitions/Column"
  },
  "type": "object"
}

I think it should be this:

{
  "patternProperties": {
    "^[0-9]+$": { "$ref": "#/definitions/Column" }
  },
  "type": "object"
}

[domoritz]

It's it incorrect but could be more narrow. Happy to review a pull request that improves this.