Restore date field.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46430 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rss/maker/base.rb

@@ -367,7 +367,7 @@ module RSS
         self.date ||= self.dc_date
         super
       ensure
-        date = keep[:date]
+        self.date = keep[:date]
         dc_dates.replace(keep[:dc_dates])
       end