Bump @antora/site-generator-default from 2.3.3 to 2.3.4 in /docs (#8)

Bumps [@antora/site-generator-default](https://gitlab.com/antora/antora) from 2.3.3 to 2.3.4.
- [Release notes](https://gitlab.com/antora/antora/tags)
- [Changelog](https://gitlab.com/antora/antora/blob/master/CHANGELOG.adoc)
- [Commits](https://gitlab.com/antora/antora/compare/v2.3.3...v2.3.4)

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