Update deprecated config name

Author: nygrenh

config/environments/production.rb

@@ -24,7 +24,7 @@
   # config.action_dispatch.rack_cache = true
 
   # Disable Rails's static asset server (Apache or nginx will already do this).
-  config.serve_static_assets = false
+  config.serve_static_files = false
 
   # Compress JavaScripts and CSS.
   config.assets.js_compressor = :uglifier