Fix instance of class in express language in DI

It's not a ContainerBuilder but a Container instance usable in complex expr

Author: mocrates

service_container/expression_language.rst

@@ -64,7 +64,7 @@ In this context, you have access to 2 functions:
 ``parameter``
     Returns a specific parameter value (syntax is just like ``service``).
 
-You also have access to the :class:`Symfony\\Component\\DependencyInjection\\ContainerBuilder`
+You also have access to the :class:`Symfony\\Component\\DependencyInjection\\Container`
 via a ``container`` variable. Here's another example:
 
 .. configuration-block::