fix(mRepsonse): mResponseError contains a body not a _source property

[QuentinRousselet]

What does this PR do ?

This PR corrects the type of mResponseError as it returns a

  document: {
    _id: string;
    body: JSONObject;
  };

and doesn't have any _source property

[kuzzle]

🎉 This PR is included in version 7.15.1-beta.1 🎉

The release is available on:

• npm package (@beta dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[kuzzle]

🎉 This PR is included in version 7.15.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀