Fix additional properties

[shtrihstr]

According the documentation https://spacetelescope.github.io/understanding-json-schema/reference/object.html

If additionalProperties is an object, that object is a schema that will be used to validate any additional properties not listed in properties.

{
  "type": "object",
  "properties": {
    "number":      { "type": "number" },
    "street_name": { "type": "string" },
    "street_type": { "type": "string",
                     "enum": ["Street", "Avenue", "Boulevard"]
                   }
  },
  "additionalProperties": { "type": "string" }
}

[tlivings]

Can you add a test that validates this?

[tlivings]

Thanks for the PR @shtrihstr - can you add tests?