fix annoying bug in unbind()

By looking at commit 9943484309743c255e7478eec88764b6fba7d09e in EM
it seems that class.originalmethod(:unbind) is probably returning
info about _that_ newly added unbind method and that the documentation
in EM is lacking / not updated.

lib/em-irc/client.rb

@@ -167,7 +167,8 @@ def ready
       end
 
       # @private
-      def unbind(ignored)
+      def unbind(reason)
+        log Logger::INFO "Unbind reason: #{reason}" if reason != nil
         trigger(:disconnect)
       end