/usr/lib/ is in ruby-raindrops 0.17.0-1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/raindrops/
/usr/lib/ruby/vendor_ruby/raindrops/aggregate/
/usr/lib/ruby/vendor_ruby/raindrops/aggregate/last_data_recv.rb
/usr/lib/ruby/vendor_ruby/raindrops/aggregate/pmq.rb
/usr/lib/ruby/vendor_ruby/raindrops/aggregate.rb
/usr/lib/ruby/vendor_ruby/raindrops/last_data_recv.rb
/usr/lib/ruby/vendor_ruby/raindrops/linux.rb
/usr/lib/ruby/vendor_ruby/raindrops/middleware/
/usr/lib/ruby/vendor_ruby/raindrops/middleware/proxy.rb
/usr/lib/ruby/vendor_ruby/raindrops/middleware.rb
/usr/lib/ruby/vendor_ruby/raindrops/struct.rb
/usr/lib/ruby/vendor_ruby/raindrops/watcher.rb
/usr/lib/ruby/vendor_ruby/raindrops.rb
/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/raindrops_ext.so