/usr/lib/x86_64-linux-gnu/liblua5.1-rex-onig.so is in lua-rex-onig-dev 2.7.2-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/liblua5.1-rex-onig.so.0.0.0
/usr/lib/x86_64-linux-gnu/liblua5.1-rex-onig.so.0.0.0