Fix indentation

Co-Authored-By: Oskar Stark <oskarstark@googlemail.com>

Author: gisostallenberg

mailer.rst

@@ -161,7 +161,8 @@ An ``Address`` can be created from a single string::
 
      $email = (new Email())
         ->from(Address::fromString('Fabien <fabien@example.com>'))
-    // ...
+
+        // ...
     ;