minor symfony#9574 Fix YAML indentation (enekochan)

This PR was submitted for the master branch but it was merged into the 3.4 branch instead (closes symfony#9574).

Discussion
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Fix YAML indentation

As above.

I've targeted master as the service class definition changed since 2.7.

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Commits
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acbbd85 Fix YAML identation

Author: xabbuh

service_container/lazy_services.rst

@@ -52,8 +52,8 @@ You can mark the service as ``lazy`` by manipulating its definition:
     .. code-block:: yaml
 
         services:
-           AppBundle\Twig\AppExtension:
-             lazy:  true
+            AppBundle\Twig\AppExtension:
+                lazy:  true
 
     .. code-block:: xml