minor symfony#10957 Fix of old service ids styles to class name (SenseException)

This PR was merged into the 3.4 branch.

Discussion
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Fix of old service ids styles to class name

The docs for the service decoration used the old service ids while the FQCN ones are shown in the code examples. This PR fixed these.

Commits
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47e01ad Fix of old service ids styles to class name

Author: javiereguiluz

service_container/service_decoration.rst

@@ -51,8 +51,8 @@ When overriding an existing definition, the original service is lost:
 Most of the time, that's exactly what you want to do. But sometimes,
 you might want to decorate the old one instead (i.e. apply the `Decorator pattern`_).
 In this case, the old service should be kept around to be able to reference
-it in the new one. This configuration replaces ``app.mailer`` with a new one,
-but keeps a reference of the old one as ``app.decorating_mailer.inner``:
+it in the new one. This configuration replaces ``App\Mailer`` with a new one,
+but keeps a reference of the old one as ``App\DecoratingMailer.inner``:
 
 .. configuration-block::