Update XML snippet in "Define Services with a Custom Tag" section

RageZBla · xabbuh · commit e0eac57b641c · 2019-10-21T09:28:32.000+02:00
diff --git a/service_container/tags.rst b/service_container/tags.rst
@@ -215,7 +215,7 @@ For example, you may add the following transports as services:
                     <tag name="app.mail_transport"/>
                 </service>
 
-                <service class="\Swift_SendmailTransport">
+                <service id="Swift_SendmailTransport">
                     <tag name="app.mail_transport"/>
                 </service>
             </services>
