downloader.rb: use File.read instead of IO.read

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67591 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/downloader.rb

@@ -82,7 +82,7 @@ class Downloader
           index_options = options.dup
           index_options[:cache_save] = false # TODO: make sure caching really doesn't work for index file
           index_file = super(UNICODE_PUBLIC+name_dir_part, "#{name_dir_part}index.html", dir, true, index_options)
-          INDEX[:index] = IO.read index_file
+          INDEX[:index] = File.read(index_file)
         end
         file_base = File.basename(name, '.txt')
         return if file_base == '.' # Use pre-generated headers and tables