tool/downloader.rb: don't suppress exception

on the end of retry failure.

Fixed mistake in r61498

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61499 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/downloader.rb

@@ -277,6 +277,8 @@ class Downloader
         $stderr.puts "retrying #{e.class} (#{e.message}) after #{times ** 2} seconds..."
         sleep(times ** 2)
         retry
+      else
+        raise
       end
     end
   end