style(rubocop): remaining offences

app/models/domain.rb

@@ -85,7 +85,7 @@ class Domain < ApplicationRecord
   def parent_domains
     parts = name.split(".")
     parts[0, parts.size - 1].each_with_index.map do |_, i|
-      parts[i..-1].join(".")
+      parts[i..].join(".")
     end
   end