FIX: don't onebox to IP addresses

lib/onebox/engine/whitelisted_generic_onebox.rb

@@ -1,10 +1,12 @@
+require "ipaddr"
+
 module Onebox
   module Engine
     class WhitelistedGenericOnebox
 
       # overwrite the whitelist
       def self.===(other)
-        true
+        other.is_a?(URI) ? (IPAddr.new(other.hostname) rescue nil).nil? : true
       end
 
       # ensure we're the last engine to be used