fix mongoid bug: do not serialize cookies with json

This is somewhat explained here:

heartcombo/devise#2949

but it is because how mongoid creates that $oid and devise doesn't
like it.

Signed-off-by: zeljko <zeljko@zwr.fi>

config/initializers/cookies_serializer.rb

@@ -1,3 +1,3 @@
 # Be sure to restart your server when you modify this file.
 
-Rails.application.config.action_dispatch.cookies_serializer = :json
+# Rails.application.config.action_dispatch.cookies_serializer = :json