[DRE-maint] Bug#818461: missing dependencies on ruby modules

[Matthias Klose]

Package: src:ruby-rails-assets-favico.js
Version: 0.3.9~dfsg-3
Severity: serious
Tags: sid stretch

The package is missing dependencies on ruby modules, seen in
https://ci.debian.net/data/packages/unstable/amd64/r/ruby-rails-assets-favico.js/latest-autopkgtest/log.gz

This is not just failing the autopkg test, but the package won't work when 
installed. Just adding ruby-sass-rails is not good enough, there are showing up 
more missing dependencies.