Fix photo link URL.

lib/jekyll/migrators/tumblr.rb

@@ -60,7 +60,9 @@ module Jekyll
           max_size = post.keys.map{ |k| k.gsub("photo-url-", "").to_i }.max
           url = post["photo-url"] || post["photo-url-#{max_size}"]
           content = "<img src=\"#{save_file(url)}\"/>"
-          content = "<a href=\"#{url}\">#{content}</a>" unless url.nil?
+          unless post["photo-link-url"].nil?
+            content = "<a href=\"#{post["photo-link-url"]}\">#{content}</a>"
+          end
         when "audio"
           if !post["id3-title"].nil?
             title = post["id3-title"]