BLD: Upgrade numpy from 1.8.0 -> 1.8.1
BLD: Upgrade numpy from 1.8.0 -> 1.8.1

Keep numpy package up to date.
1.8.1 is a bug fix release, so should be no breaking changes.

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