fix: unwrapFieldTypeName

[DorianGrey11]

In some cases, the unwrapFieldTypeName function returned null because an object was too nested.
This resulted in a TypeError [Error]: Cannot read properties of undefined.

I have adapted the tests to demonstrate this by simply having a [Book!]! return type.
In the example, the field object looks like this:

{
  "kind": "NON_NULL",
  "name": null,
  "ofType": {
    "kind": "LIST",
    "name": null,
    "ofType": {
      "kind": "NON_NULL",
      "name": null,
      "ofType": {
        "kind": "OBJECT",
        "name": "Book",
        "ofType": null
      }
    }
  }
}

The previous approach would return field.type.ofType.ofType.name, which is still null instead of the desired Book type. In order to fix this, I made the unwrapFieldTypeName function work recursively.

[mcollina]

lgtm

[mcollina]

thanks!!