Updated CHANGES.md for 0.3.9
Updated CHANGES.md for 0.3.9

NiteshKant/RxNetty,mgajdos/RxNetty,isururanawaka/RxNetty,brharrington/RxNetty,eonezhang/RxNetty,thinker0/RxNetty,mikeweisskopf/RxNetty,pieces029/RxNetty,isururanawaka/RxNetty,stevegury/RxNetty,rstoyanchev/RxNetty,NiteshKant/RxNetty,ReactiveX/RxNetty,tempbottle/RxNetty,brharrington/RxNetty,ReactiveX/RxNetty,NiteshKant/RxNetty,rstoyanchev/RxNetty,mgajdos/RxNetty,stevegury/RxNetty,mikeweisskopf/RxNetty,eonezhang/RxNetty,tempbottle/RxNetty,ReactiveX/RxNetty,thinker0/RxNetty,brharrington/RxNetty