add working_directory parameter to unicorn_config

set it to #{deploy_to}/current in application cookbook

recipes/unicorn.rb

@@ -31,6 +31,7 @@ node.set[:unicorn][:options] = { :tcp_nodelay => true, :backlog => 100 }
 
 unicorn_config "/etc/unicorn/#{app['id']}.rb" do
   listen({ node[:unicorn][:port] => node[:unicorn][:options] })
+  working_directory File.join(app['deploy_to'], 'current')
   worker_timeout node[:unicorn][:worker_timeout] 
   preload_app node[:unicorn][:preload_app] 
   worker_processes node[:unicorn][:worker_processes]