update #1866 limit sankakucomplex subdomains

followe up to 1119211db098737fa33deb03f2caae0355d1b39d; limit to available subdomains, only c3 is in the database so far

app/models/post.rb

@@ -315,7 +315,7 @@ class Post < ActiveRecord::Base
       when %r{\Ahttps?://s(?:content|photos)-[^/]+\.fbcdn.net/hphotos-.+/\d+_(\d+)_\d+_[no]\.}i
         "https://www.facebook.com/photo.php?fbid=#{$1}"
 
-      when %r{\Ahttp://c(?:s|han|\d{1}).sankakucomplex.com/data(?:/sample)?/(?:[a-f0-9]{2}/){2}(?:sample-|preview)?([a-f0-9]{32})}i
+      when %r{\Ahttp://c(?:s|han|[1-4]).sankakucomplex.com/data(?:/sample)?/(?:[a-f0-9]{2}/){2}(?:sample-|preview)?([a-f0-9]{32})}i
         "http://chan.sankakucomplex.com/en/post/show?md5=#{$1}"
 
       else