Remove pid configuration from unicorn config

Fixes restart issue of the single-process image because the pid file was
already written in the previous run. Since we only start one server we
don't need to track it's pid.

docker/scripts/setup_env

@@ -89,5 +89,6 @@ cp -a config/unicorn.rb.example config/unicorn.rb
 sed -ri 's/^listen .*$/listen ENV["PORT"]/' config/unicorn.rb
 sed -ri 's/^stderr_path.*$//' config/unicorn.rb
 sed -ri 's/^stdout_path.*$//' config/unicorn.rb
+sed -ri 's/^pid.*$//' config/unicorn.rb
 
 mkdir -p tmp/pids tmp/cache tmp/sockets log