Different load for Rails

Directly taken from gzigzigzeo#41
There's a potential issue with the initialization that prevents the
config to be correctly loaded when in Rails.
This enforces the right timing

Author: elcuervo

lib/sidekiq/grouping.rb

@@ -57,4 +57,8 @@ def start!
   end
 end
 
-Sidekiq::Grouping.start! if Sidekiq.server?
+if defined?(Rails)
+  require "sidekiq/grouping/railtie"
+else
+  Sidekiq::Grouping.start! if Sidekiq.server?
+end

lib/sidekiq/grouping/railtie.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+module Sidekiq
+  module Grouping
+    class Railtie < ::Rails::Railtie
+      config.after_initialize do
+        Sidekiq::Grouping.start! if Sidekiq.server?
+      end
+    end
+  end
+end