fix Redmine::Themes#scan_themes is not private

git-svn-id: http://svn.redmine.org/redmine/trunk@18578 e93f8b46-1217-0410-a6f0-8f06a7374b81

.rubocop_todo.yml

@@ -606,7 +606,6 @@ Lint/UriEscapeUnescape:
 Lint/UselessAccessModifier:
   Exclude:
     - 'app/models/changeset.rb'
-    - 'lib/redmine/themes.rb'
 
 Lint/UselessAssignment:
   Enabled: false

lib/redmine/themes.rb

@@ -132,8 +132,6 @@ module Redmine
       end
     end
 
-    private
-
     def self.scan_themes
       dirs = Dir.glob("#{Rails.public_path}/themes/*").select do |f|
         # A theme should at least override application.css
@@ -141,5 +139,6 @@ module Redmine
       end
       dirs.collect {|dir| Theme.new(dir)}.sort
     end
+    private_class_method :scan_themes
   end
 end