[book][service_container] Tweaking syntax for import - is more common, doesn't use the unneeded key

Author: weaverryan

book/service_container.rst

@@ -390,8 +390,7 @@ configuration.
 
         # app/config/config.yml
         imports:
-            hello_bundle:
-                resource: @AcmeHelloBundle/Resources/config/services.yml
+            - { resource: @AcmeHelloBundle/Resources/config/services.yml }
 
     .. code-block:: xml