/usr/lib/ruby/ is in ruby-em-mongo 0.5.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/em-mongo.rb
/usr/lib/ruby/vendor_ruby/em-mongo/
/usr/lib/ruby/vendor_ruby/em-mongo/support.rb
/usr/lib/ruby/vendor_ruby/em-mongo/server_response.rb
/usr/lib/ruby/vendor_ruby/em-mongo/exceptions.rb
/usr/lib/ruby/vendor_ruby/em-mongo/collection.rb
/usr/lib/ruby/vendor_ruby/em-mongo/conversions.rb
/usr/lib/ruby/vendor_ruby/em-mongo/core_ext.rb
/usr/lib/ruby/vendor_ruby/em-mongo/prev.rb
/usr/lib/ruby/vendor_ruby/em-mongo/database.rb
/usr/lib/ruby/vendor_ruby/em-mongo/VERSION
/usr/lib/ruby/vendor_ruby/em-mongo/request_response.rb
/usr/lib/ruby/vendor_ruby/em-mongo/connection.rb
/usr/lib/ruby/vendor_ruby/em-mongo/cursor.rb