update mdbook for devdocs to 0.4.15
Description
update the mdbook image to version 0.4.15
Goal
Evidence
Solution
Links / references
https://github.com/peaceiris/docker-mdbook/releases/tag/v0.4.15
update the mdbook image to version 0.4.15
https://github.com/peaceiris/docker-mdbook/releases/tag/v0.4.15