Allow nested fragments

[cooperka]

Example query:

query items {
  items {
    ...Foo
  }
}

fragment Foo on Item {
  name
  ...Bar
}

fragment Bar on Item {
  description
}

Currently, neo4j-graphql-js returns only part of the desired data:

"items": [
  {
    "name": "My name",
    "description": null
  }
]

Effectively ignoring the nested fragment. This simple change allows it to check fragments for nested fragments and return that data as well.

[johnymontana]

Thanks @cooperka!