minor #8022 Fixed app/config/services.yml link (Walkoss)

This PR was merged into the 3.3 branch.

Discussion
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Fixed app/config/services.yml link

The link for [Symfony Standard Edition (version 3.3) services.yml](https://github.com/symfony/symfony-standard/blob/master/app/config/services.yml) is not found on Github because there is no master branch for `symfony/symfony-standard` so I updated it to branch version [3.3](https://github.com/symfony/symfony-standard/blob/3.3/app/config/services.yml)

Commits
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884d0b4 Fixed app/config/services.yml link

Author: weaverryan

service_container.rst

@@ -1002,4 +1002,4 @@ Learn more
     /service_container/*
 
 .. _`service-oriented architecture`: https://en.wikipedia.org/wiki/Service-oriented_architecture
-.. _`Symfony Standard Edition (version 3.3) services.yml`: https://github.com/symfony/symfony-standard/blob/master/app/config/services.yml
+.. _`Symfony Standard Edition (version 3.3) services.yml`: https://github.com/symfony/symfony-standard/blob/3.3/app/config/services.yml