Make sure Rabl is using Oj

config/initializers/rabl_init.rb

@@ -1,4 +1,5 @@
 Rabl.configure do |config|
+  config.json_engine       = Oj
   config.cache_all_output  = false
   config.cache_sources     = Rails.env.production?
   config.include_json_root = false