BLD: Upgrade six library to 1.6.1
BLD: Upgrade six library to 1.6.1

From 1.5.2 -> 1.6.1

Keep package up to date.

alphaBenj/zipline,MonoCloud/zipline,morrisonwudi/zipline,ronalcc/zipline,grundgruen/zipline,cmorgan/zipline,jordancheah/zipline,AlirezaShahabi/zipline,mattcaldwell/zipline,otmaneJai/Zipline,keir-rex/zipline,alphaBenj/zipline,jimgoo/zipline-fork,nborggren/zipline,enigmampc/catalyst,grundgruen/zipline,MonoCloud/zipline,umuzungu/zipline,ronalcc/zipline,bartosh/zipline,StratsOn/zipline,otmaneJai/Zipline,sketchytechky/zipline,michaeljohnbennett/zipline,humdings/zipline,erikness/AlephOne,jordancheah/zipline,stkubr/zipline,zhoulingjun/zipline,gwulfs/zipline,gwulfs/zipline,cmorgan/zipline,keir-rex/zipline,zhoulingjun/zipline,iamkingmaker/zipline,aajtodd/zipline,wilsonkichoi/zipline,humdings/zipline,nborggren/zipline,magne-max/zipline-ja,dkushner/zipline,quantopian/zipline,chrjxj/zipline,CDSFinance/zipline,AlirezaShahabi/zipline,jimgoo/zipline-fork,magne-max/zipline-ja,euri10/zipline,wilsonkichoi/zipline,aajtodd/zipline,YuepengGuo/zipline,semio/zipline,DVegaCapital/zipline,mattcaldwell/zipline,michaeljohnbennett/zipline,CDSFinance/zipline,joequant/zipline,stkubr/zipline,StratsOn/zipline,quantopian/zipline,florentchandelier/zipline,erikness/AlephOne,florentchandelier/zipline,ChinaQuants/zipline,dhruvparamhans/zipline,enigmampc/catalyst,iamkingmaker/zipline,euri10/zipline,Scapogo/zipline,dkushner/zipline,bartosh/zipline,morrisonwudi/zipline,YuepengGuo/zipline,dmitriz/zipline,Scapogo/zipline,sketchytechky/zipline,kmather73/zipline,semio/zipline,wubr2000/zipline,ChinaQuants/zipline,chrjxj/zipline,dmitriz/zipline,wubr2000/zipline,kmather73/zipline,dhruvparamhans/zipline,joequant/zipline,DVegaCapital/zipline,umuzungu/zipline