/usr/include/x86_64-linux-gnu/ruby-2.3.0/libRuby.so is in libroot-bindings-ruby-dev 5.34.30-0ubuntu8.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/include/x86_64-linux-gnu/ruby-2.3.0/../../../lib/x86_64-linux-gnu/root5.34/libRuby.so