Changed os detection to RbConfig which works with jruby
Changed os detection to RbConfig which works with jruby

Added a proper require 'rbconfig'

dannyfallon/dalli,akihiro17/dalli,eagletmt/dalli,mperham/dalli,indirect/dalli,wjordan/dalli,hirocaster/dalli,petergoldstein/dalli,dtakahas/dalli,eileencodes/dalli,mumoshu/dalli,exact/dalli,petergoldstein/dalli