don't use unicorn worker killer if PhusionPassenger is defined

config.ru

 # This file is used by Rack-based servers to start the application.
-# Unicorn self-process killer
-require 'unicorn/worker_killer'
-# # Max memory size (RSS) per worker
-use Unicorn::WorkerKiller::Oom, (200 * (1 << 20)), (250 * (1 << 20))
+unless defined?(PhusionPassenger)
+  # Unicorn self-process killer
+  require 'unicorn/worker_killer'
+  # Max memory size (RSS) per worker
+  use Unicorn::WorkerKiller::Oom, (200 * (1 << 20)), (250 * (1 << 20))
+end
 require ::File.expand_path('../config/environment',  __FILE__)