Fixes Markdown links in README.
Fixes Markdown links in README.

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