bug #4147 [Cookbook][Logging] add missing Monolog handler type in XML…

… config (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
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[Cookbook][Logging] add missing Monolog handler type in XML config

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

Omitting the type of a handler leads to an error:

> Symfony\Component\Config\Definition\Exception\InvalidConfigurationException: The child node "type" at path "monolog.handlers.swift" must be configured.

Commits
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dc33b0c add missing Monolog handler type in XML config

cookbook/logging/monolog_email.rst

@@ -56,6 +56,7 @@ it is broken down.
                 />
                 <monolog:handler
                     name="swift"
+                    type="swift_mailer"
                     from-email="error@example.com"
                     to-email="error@example.com"
                     subject="An Error Occurred!"