Bump chezmoi.io/themes/book from 60dfd9a to 1e4bcc2

Bumps [chezmoi.io/themes/book](https://github.com/alex-shpak/hugo-book) from `60dfd9a` to `1e4bcc2`.
- [Release notes](https://github.com/alex-shpak/hugo-book/releases)
- [Commits](alex-shpak/hugo-book@60dfd9a...1e4bcc2)

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