/usr/lib/x86_64-linux-gnu/libonig.so is in libonig-dev 5.9.5-3.2+deb8u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libonig.so.2.0.1
/usr/lib/x86_64-linux-gnu/libonig.so.2.0.1