/usr/lib/ is in ruby-pg 0.18.4-1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/x86_64-linux-gnu/
/usr/lib/x86_64-linux-gnu/ruby/
/usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/
/usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/2.3.0/
/usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/2.3.0/pg_ext.so
/usr/lib/ruby/
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/pg.rb
/usr/lib/ruby/vendor_ruby/pg/
/usr/lib/ruby/vendor_ruby/pg/connection.rb
/usr/lib/ruby/vendor_ruby/pg/type_map_by_column.rb
/usr/lib/ruby/vendor_ruby/pg/text_decoder.rb
/usr/lib/ruby/vendor_ruby/pg/result.rb
/usr/lib/ruby/vendor_ruby/pg/constants.rb
/usr/lib/ruby/vendor_ruby/pg/basic_type_mapping.rb
/usr/lib/ruby/vendor_ruby/pg/exceptions.rb
/usr/lib/ruby/vendor_ruby/pg/coder.rb
/usr/lib/ruby/vendor_ruby/pg/text_encoder.rb