Bump assets/chezmoi.io/themes/book from e939f40 to 50147be

Bumps [assets/chezmoi.io/themes/book](https://github.com/alex-shpak/hugo-book) from `e939f40` to `50147be`.
- [Release notes](https://github.com/alex-shpak/hugo-book/releases)
- [Commits](alex-shpak/hugo-book@e939f40...50147be)

---
updated-dependencies:
- dependency-name: assets/chezmoi.io/themes/book
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>