Restore puma_bind setting removed in capistrano3-puma 6.0.0

In earlier versions of capistrano3-puma, the puma_bind has a default value to:
unix://.../tmp/sockets/puma.sock via set_if_empty in lib/capistrano/puma.rb.

This default was removed in 6.0.0, requiring to explicitly set :puma_bind in deploy.rb.

This caused the following runtime error during deploy:
> Failed to restart consul_puma_staging.service: Unit
> consul_puma_staging.socket has a bad unit file setting.

config/deploy.rb

@@ -53,6 +53,7 @@ set :puma_conf, "#{release_path}/config/puma/#{fetch(:rails_env)}.rb"
 set :puma_systemctl_user, :user
 set :puma_enable_socket_service, true
 set :puma_service_unit_env_vars, ["EXECJS_RUNTIME=Disabled"]
+set :puma_bind, "unix://#{shared_path}/tmp/sockets/puma.sock"
 
 set :delayed_job_workers, 2
 set :delayed_job_roles, :background