[config][translator] use the new fallbacks option.

Author: aitboudad

app/config/config.yml

@@ -4,7 +4,7 @@ imports:
 
 framework:
     #esi:             ~
-    #translator:      { fallback: "%locale%" }
+    #translator:      { fallbacks: ["%locale%"] }
     secret:          "%secret%"
     router:
         resource: "%kernel.root_dir%/config/routing.yml"