minor symfony#4212 Missing backtick, thanks to @Baptouuuu (WouterJ)

This PR was merged into the 2.5 branch.

Discussion
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Missing backtick, thanks to @Baptouuuu

See symfony#4134

Commits
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dadaea3 Missing backtick, thanks to @Baptouuuu

Author: weaverryan

components/dependency_injection/advanced.rst

@@ -269,7 +269,7 @@ a reference of the old one  as ``bar.inner``:
             ->setPublic(false)
             ->setDecoratedService('foo');
 
-Here is what's going on here: the ``setDecoratedService()` method tells
+Here is what's going on here: the ``setDecoratedService()`` method tells
 the container that the ``bar`` service should replace the ``foo`` service,
 renaming ``foo`` to ``bar.inner``.
 By convention, the old ``foo`` service is going to be renamed ``bar.inner``,