Retry downloads more for unicode outage

like https://ci.appveyor.com/project/ruby/ruby/builds/24142523/job/v6aq4srj7c3hgt86

tool/downloader.rb

@@ -192,7 +192,7 @@ class Downloader
       $stdout.flush
     end
     begin
-      data = with_retry(6) do
+      data = with_retry(9) do
         url.read(options.merge(http_options(file, since.nil? ? true : since)))
       end
     rescue OpenURI::HTTPError => http_error