Deep translation structure breaks generating gatsby types for Translation

[FrEaKmAn]

Describe the bug
If we have a translation with deep structure, like

{
  "languages": {
     "en": "English",
     "de": "Deutsch"
  }
}

it fails to generate correct Translation type in gatsby-types.d.ts. The translation is missing message.

To Reproduce
Steps to reproduce the behavior:

1. Add example above as messages for any locale.
2. Run build.
3. Check gatsby-types.d.ts

Expected behavior

The Translation type should include

  readonly message: Maybe<Scalars['String']>;

[openscript]

Thank you for reporting! As I completely migrated away from Gatsby, I don't want to invest further time into this, but I'm happy to merge and release a PR. :)