[DRE-maint] ruby-mini-magick is marked for autoremoval from testing

[Debian testing autoremoval watch]

ruby-mini-magick 4.8.0-1 is marked for autoremoval from testing on 2018-03-26

It (build-)depends on packages with these RC bugs:
890042: ruby-posix-spawn: ruby-posix-spawn is broken on 32bit architectures