Adding string: processor

Author: ThomasLandauer

mailer.rst

@@ -33,7 +33,7 @@ over SMTP by configuring the DSN in your ``.env`` file (the ``user``,
         # config/packages/mailer.yaml
         framework:
             mailer:
-                dsn: '%env(MAILER_DSN)%'
+                dsn: '%env(string:MAILER_DSN)%'
 
     .. code-block:: xml
 
@@ -47,7 +47,7 @@ over SMTP by configuring the DSN in your ``.env`` file (the ``user``,
                 http://symfony.com/schema/dic/symfony https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">
 
             <framework:config>
-                <framework:mailer dsn="%env(MAILER_DSN)%"/>
+                <framework:mailer dsn="%env(string:MAILER_DSN)%"/>
             </framework:config>
         </container>