Revert "switch from http to https for Unicode data file downloads"

This reverts commit 90de118a75.

  The environment of mswinci couldn't handle https download.
  (It's certificates problem, We should upgrade its environment)

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61169 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/downloader.rb

@@ -71,7 +71,7 @@ class Downloader
 
   class Unicode < self
     def self.download(name, *rest)
-      super("https://www.unicode.org/Public/#{name}", name, *rest)
+      super("http://www.unicode.org/Public/#{name}", name, *rest)
     end
   end