Fixed a missed reference

Author: javiereguiluz

templating/twig_extension.rst

@@ -72,6 +72,8 @@ you're done! Symfony will automatically know about your new service and add the
 
 You can now start using your filter in any Twig template.
 
+.. _lazy-loaded-twig-extensions:
+
 Creating Lazy-Loaded Twig Extensions
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