community/aercbook: upgrade to 0.1.6

https://github.com/renerocksai/aercbook/compare/v0.1.5...v0.1.6

Update source url to use git commit hash since the git.sr.ht repo no longer exists and the GitHub repo currently does not have tags. New source found thanks to @fossdd. Resolves rebuild failure on the 3.21 builders due to 404 error (error log).

Was able to confirm through the Wayback Machine that the latest commit in GitHub was made at or after version 0.1.5, though could not determine whether it is the exact version, so pkgver includes the _git suffix.

Fixes #16652 (closed)