Add RuboCop 1.81

Author: bbatsov

antora-playbook.yml

@@ -1,7 +1,7 @@
 site:
   title: RuboCop Docs
   url: https://docs.rubocop.org/
-  start_page: 1.80@rubocop::index.adoc
+  start_page: 1.81@rubocop::index.adoc
   keys:
     google_analytics: "UA-140153536-1"
 urls:
@@ -34,6 +34,7 @@ content:
           "v1.78.0",
           "v1.79.0",
           "v1.80.0",
+          "v1.81.1",
         ]
       start_path: docs
     - url: https://github.com/rubocop/rubocop-ast.git