/usr/lib/x86_64-linux-gnu/libruby-2.1.so is in ruby2.1-dev 2.1.5-2+deb8u3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libruby-2.1.so.2.1.0
/usr/lib/x86_64-linux-gnu/libruby-2.1.so.2.1.0