Change html+twig code-block to twig

Author: nicwortel

frontend/asset_mapper.rst

@@ -1077,7 +1077,7 @@ used to pass attributes to the rendered ``<script>`` tags.
 You can use the `NelmioSecurityBundle`_ to generate the nonce and include
 it in the CSP header, and then pass the same nonce to the Twig function:
 
-.. code-block:: html+twig
+.. code-block:: twig
 
     {{ importmap('app', {'nonce': csp_nonce('script')}) }}