minor symfony#6954 Typo fix in tags.rst (NoScopie)

This PR was merged into the 2.8 branch.

Discussion
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Typo fix in tags.rst

I think there is a typo with acme_mailer.transport, this should be app.mail_transport since you are using the app.mail_transport on any other place.

Commits
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2fecab5 Update tags.rst

Author: xabbuh

service_container/tags.rst

@@ -195,7 +195,7 @@ Create a Compiler Pass
 ~~~~~~~~~~~~~~~~~~~~~~
 
 You can now use a :ref:`compiler pass <components-di-separate-compiler-passes>` to ask the
-container for any services with the ``acme_mailer.transport`` tag::
+container for any services with the ``app.mail_transport`` tag::
 
     // src/AppBundle/DependencyInjection/Compiler/MailTransportPass.php
     namespace AppBundle\DependencyInjection\Compiler;