god doesn't stop unicorn

I have this file

rails_env = ENV['RAILS_ENV'] || 'development'
rails_root = ENV['RAILS_ROOT'] || "/home/luiz/rails_dev/api"

God.watch do |w|
  w.name = "unicorn"
  w.interval = 30.seconds # default

  # unicorn needs to be run from the rails root
  w.start = "cd #{rails_root} && unicorn_rails -c config/unicorn.rb -E #{rails_env}"

  # QUIT gracefully shuts down workers
  w.stop = "kill -QUIT `cat #{rails_root}/tmp/pids/unicorn.pid`"

  # USR2 causes the master to re-create itself and spawn a new worker pool
  w.restart = "kill -USR2 `cat #{rails_root}/tmp/pids/unicorn.pid`"

  w.start_grace = 10.seconds
  w.restart_grace = 10.seconds
  w.pid_file = "#{rails_root}/tmp/pids/unicorn.pid"

  w.behavior(:clean_pid_file)

  w.start_if do |start|
    start.condition(:process_running) do |c|
      c.interval = 5.seconds
      c.running = false
    end
  end

  w.restart_if do |restart|
    restart.condition(:memory_usage) do |c|
      c.above = 300.megabytes
      c.times = [3, 5] # 3 out of 5 intervals
    end

    restart.condition(:cpu_usage) do |c|
      c.above = 50.percent
      c.times = 5
    end
  end

  # lifecycle
  w.lifecycle do |on|
    on.condition(:flapping) do |c|
      c.to_state = [:start, :restart]
      c.times = 5
      c.within = 5.minute
      c.transition = :unmonitored
      c.retry_in = 10.minutes
      c.retry_times = 5
      c.retry_within = 2.hours
    end
  end
end

I start unicorn with god -c unicorn.god -D -p 8081 and my workers are setup fine. but, sometimes I need do stop unicorn (god stop unicorn -p 8081 in another console) but the server keep up and running.
what am I missing?

Edit

We're moving from unicorn to puma (not because this question, it's a performance thing), and not going to use god anymore...thanks everybody for your help

Now we are using foreman and puma right now...this is our initializer:
web: bundle exec puma -q -d -e production -b 'unix:///home/api/shared/web.socket' -S /home/api/shared/web.state --control 'unix:///home/api/shared/web.ctl'

and deploying with capistrano, so that we can stop and restart the server like this

config/deploy.rb

# Puma commands
_cset(:puma_cmd) { "#{fetch(:bundle_cmd, 'bundle')} exec puma" }
_cset(:pumactl_cmd) { "#{fetch(:bundle_cmd, 'bundle')} exec pumactl" }
_cset(:puma_state) { "#{shared_path}/puma.state" }
_cset(:puma_role) { :app }

# Puma
namespace :puma do

  desc 'Start puma'
  task :start do
    run "cd #{current_path} ; bundle exec foreman start web"
  end

  desc 'Stop puma'
  task :stop, :roles => lambda { fetch(:puma_role) }, :on_no_matching_servers => :continue do
    run "cd #{current_path} && #{fetch(:pumactl_cmd)} -S #{fetch(:puma_state)} stop"
  end

  desc 'Restart puma'
  task :restart, :roles => lambda { fetch(:puma_role) }, :on_no_matching_servers => :continue do
    run "cd #{current_path} && #{fetch(:pumactl_cmd)} -S #{fetch(:puma_state)} restart"
  end
end