Made corrections for LibriVox

[siesto1elemento]

Motivation and context

made a mistake, not initializing the language_id_mapping for LibriVox.

How has this been tested?

Tested using insomnia HTTP client, returned rq_id and 202 accepted message

Checklist

• I submit my changes into the develop branch
• I have created a changelog fragment
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (see GitHub docs)
• I have increased versions of npm packages if it is necessary
  (cvat-canvas,
  cvat-core,
  cvat-data and
  cvat-ui)

License

• [ x] I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.