Update core/dto.md

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

Author: dunglas

core/dto.md

@@ -351,7 +351,7 @@ use Swagger\Annotations as SWG;
     public function __invoke()
 ```
 
-### Specify an input and/or output class
+### Specify an Input and/or Output Class
 
 For a given resource class, you may want to have a different representation of this class as input (write) or output (read).
 To do so, a resource can take an input and/or an output class: