use absolute_url to generate the feed_meta url

lib/jekyll/feed_meta_tag.rb

@@ -1,5 +1,8 @@
 module Jekyll
   class FeedMetaTag < Liquid::Tag
+    # Use Jekyll's native relative_url filter
+    include Jekyll::Filters::URLFilters
+
     def render(context)
       @context = context
       attrs    = attributes.map { |k, v| %(#{k}="#{v}") }.join(" ")
@@ -16,7 +19,7 @@ def attributes
       {
         :type  => "application/atom+xml",
         :rel   => "alternate",
-        :href  => "#{url}/#{path}",
+        :href  => absolute_url(path),
         :title => title
       }.keep_if { |_, v| v }
     end
@@ -29,14 +32,6 @@ def path
       end
     end
 
-    def url
-      if config["url"]
-        URI.join(config["url"], config["baseurl"])
-      elsif config["github"] && config["github"]["url"]
-        config["github"]["url"]
-      end
-    end
-
     def title
       config["title"] || config["name"]
     end