Update mercure.rst

Co-Authored-By: dunglas <[email protected]>

Author: javiereguiluz

mercure.rst

@@ -238,7 +238,7 @@ and to use URI Templates as patterns:
 Async dispatching
 -----------------
 
-Instead of calling the `Publisher` service directly, you can also let Symfony
+Instead of calling the ``Publisher`` service directly, you can also let Symfony
 dispatching the updates asynchronously thanks to the provided integration with
 the Messenger component.