fixes previous pull request : completion of the example of multiple entinty with mappings

Author: carlossg00

book/doctrine/orm/configuration.rst

@@ -167,11 +167,13 @@ The following configuration code shows how to define two EntityManagers:
  entity_managers:
  default:
  connection: default
- mappings: MyBundle1: ~
- mappings: MyBundle2: ~
+ mappings: 
+ MyBundle1: ~
+ MyBundle2: ~
  customer:
  connection: customer
- mappings: MyBundle3: ~
+ mappings:
+ MyBundle3: ~
 
 Just like the DBAL, if you have configured multiple ``EntityManager``
 instances and want to get a specific one you can use the full service name to