Celluloid running in backported mode

[ldilley]

On start, the following message is displayed:

I, [2016-11-06T11:40:26.869000 #15391] INFO -- : Celluloid 0.17.2 is running in BACKPORTED mode. [ http://git.io/vJf3J ]

Update the codebase to prepare for newer versions of Celluloid per https://github.com/celluloid/celluloid/wiki/DEPRECATION-WARNING.

[ldilley]

I am suggesting to just wait until Celluloid 1.0 is officially released prior to making any changes to RubIRCd's cell.rb module.