Use correct versionadded version

OskarStark · OskarStark · commit b5e5d4ddc8a7 · 2019-08-21T09:43:52.000+02:00
diff --git a/contributing/documentation/format.rst b/contributing/documentation/format.rst
@@ -189,7 +189,7 @@ describe how the behavior has changed:
 
 .. code-block:: rst
 
-    .. versionadded:: 4.2
+    .. versionadded:: 5.2
 
        ... ... ... was introduced in Symfony 5.2. Prior to this,
        ... ... ... ... ... ... ... ... .
