typo on subresources.md (#1912)

missing line break was causing formatting error on https://api-platform.com/docs/core/subresources/

Author: Altherius

core/subresources.md

@@ -109,6 +109,7 @@ To make things work, API Platform needs information about how to retrieve the `A
 the `Question`, this is done by configuring the `uriVariables`:
 
 <code-selector>
+
 ```php
 <?php
 // api/src/Entity/Answer.php