Fix rubocop warning

lib/tasks/upgrade_avatars.rake

@@ -1,7 +1,8 @@
 namespace "storage" do
   task :upgrade_avatars => :environment do
     User.active.where.not(:image_file_name => nil).in_batches.each_record do |user|
-      unless user.avatar.attached?
+      next if user.avatar.attached?
+
       io = File.open(user.image.path)
       filename = user.image.original_filename
       content_type = if user.image.content_type.nil?
@@ -13,5 +14,4 @@ namespace "storage" do
       user.avatar.attach(:io => io, :filename => filename, :content_type => content_type)
     end
   end
-  end
 end