/usr/share/doc/liberubis-ruby1.9.1/changelog.Debian.gz is in liberubis-ruby1.9.1 2.7.0-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/liberubis-ruby1.9.1/../ruby-erubis/changelog.Debian.gz