fix documentation link

Author: xabbuh

src/Symfony/Component/ObjectMapper/README.md

@@ -12,7 +12,7 @@ are not covered by Symfony's
 Resources
 ---------
 
- * [Documentation](https://symfony.com/doc/current/components/object-mapper.html)
+ * [Documentation](https://symfony.com/doc/current/object_mapper.html)
  * [Contributing](https://symfony.com/doc/current/contributing/index.html)
  * [Report issues](https://github.com/symfony/symfony/issues) and
    [send Pull Requests](https://github.com/symfony/symfony/pulls)