Run celluloid backported mode.

[jeyraof]

In my code, I changed code

from

require 'celluloid-io'
require 'celluloid/autostart'

to

require 'celluloid/current'
require 'celluloid-io'

because of following documentation

But warning message still poped up.

Celluloid 0.17.3 is running in BACKPORTED mode. [ http://git.io/vJf3J ]

How can i fix it?