text: Title: "Not implemented" exception in TypeRef.to_json()
  Body: Input:
  
  ```
  (Pdb) pp self.__dict__
  {'is_list': True,
   'is_list_item_nullable': True,
   'is_nullable': False,
   'kind': 'SCALAR',
   'list': True,
   'name': 'String',
   'non_null': True,
   'non_null_item': False}
  ```
  
  Output:
  
  ```
  (Pdb) where
  ...
  > /Users/nikitastupin/Documents/repos/clairvoyance/clairvoyance/graphql.py(234)to_json()
  -> raise Exception("Not implemented")
  ```
  
  Expected output:
  
  ```
  {
    "name": null,
    "kind": "NON_NULL",
    "ofType": {
      "name": null,
      "kind": "LIST",
      "ofType": {
        "name": "String",
        "kind": "SCALAR",
        "ofType": null
      }
    }
  }
  ```