Add missing variable in templates regarding toc (#127)

Related to #123 and alignement with `html_document()` behavior
diff --git a/R/utils.R b/R/utils.R
index 52381a2..7251cff 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -27,4 +27,4 @@
     }
   }
   pandoc_variable_arg(option, value)
-}
\ No newline at end of file
+}