minor symfony#13620 Update service_container.rst (zer0uno)

This PR was submitted for the 5.0 branch but it was merged into the 4.4 branch instead.

Discussion
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Update service_container.rst

if a public service should *not* be fetched by ``$container->get()``, how should it be fetched? The example shows the use of ``$container->get()``, so I think there was a typo and it should be changed from "public" => "private"

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Commits
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5317f98 Update service_container.rst

Author: javiereguiluz

service_container.rst

@@ -860,7 +860,7 @@ This is mostly useful when you want to fetch services lazily::
 
 As a best practice, you should only create *private* services, which will happen
 automatically. And also, you should *not* use the ``$container->get()`` method to
-fetch public services.
+fetch private services.
 
 But, if you *do* need to make a service public, override the ``public`` setting: