fix: load boldsymbol mathjax extension

[taharallouche]

Checklist

• [x] I have read the CONTRIBUTING document
• [x] I hereby agree to the terms of either individual CLA available at: https://toloka.ai/legal/cla_individual or corporate CLA available at: https://toloka.ai/legal/cla_corporate, whichever is applicable to me, as it pertains to direct contributions to crowd-kit only
• [x] My change requires a change to the documentation
• [ ] I have updated the documentation accordingly
• [ ] I have added tests to cover my changes
• [ ] All new and existing tests passed

[taharallouche]

Fixes #123 , I'll be happy to fix it in any other way if the maintainers have other preferences