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

[Debian testing autoremoval watch]

ruby-barby 0.6.5-1 is marked for autoremoval from testing on 2018-03-21

It (build-)depends on packages with these RC bugs:
888193: ruby-rmagick: FTBFS on ruby2.5: <FrozenError(<can't modify frozen Magick::Image>)>