Updating docs with optional `context` arg for a few methods. `groupBy`, `countBy` and `sortedIndex` can all take an optional `context` argument, but this wasn't in the docs.
Updating docs with optional `context` arg for a few methods.
`groupBy`, `countBy` and `sortedIndex` can all take an optional
`context` argument, but this wasn't in the docs.

Aplopio/underscore,thisismygithub/underscore,npmcomponent/jashkenas-underscore,dyx/underscore,ereddate/underscore,jonot/underscore,SerenoShen/underscore,PengShi-sp/underscore,starterstep/underscore,Yangani/underscore,documentcloud/underscore,lucasfanning/underscore,ijidan/underscore,debutt/underscore,jdelbello/underscore,lis186/underscore,vinodbonala/underscore,1800joe/underscore,jfarid27/underscore,yuhualingfeng/underscore,wjb12/underscore,cintiamh/underscore,jianganglu/underscore,WangRex/underscore,gougouGet/underscore,yuhualingfeng/underscore,roychen-7/underscore,dkusch/underscore,kairyan/underscore,dyx/underscore,cnwhy/underscore,jdelbello/underscore,nickkneafsey/underscore,SerenoShen/underscore,JoaquinSiabra/underscore,irr/underscore,irr/underscore,amdjs/underscore,dkusch/underscore,kuychaco/underscore,ligson/underscore,youprofit/underscore,mdboop/underscore,PUSEN/underscore,emiel187/underscore,dfurtado/underscore,Forever8/underscore,xiaoqiang730730/underscore,veg/underscore,dfurtado/underscore,jashkenas/underscore,strongconjunctions/underscore,polandeme/underscore,zhangguangyong/underscore,jianganglu/underscore,jordanwink201/underscore,JoaquinSiabra/underscore,tnga/underscore-es,lucasfanning/underscore,jfarid27/underscore,jolthoff/underscore,vinodbonala/underscore,eaglesjava/underscore,rlugojr/underscore,beenlee/underscore,janocat/underscore,Aplopio/underscore,falqas/underscore,mdboop/underscore,ThiagoGarciaAlves/underscore,huzion/underscore,ereddate/underscore,greyhwndz/underscore,jridgewell/underscore,janocat/underscore,wjb12/underscore,ryanwholey/underscore,colemakdvorak/underscore,Tim-Zhang/underscore,eaglesjava/underscore,AaronNGray/underscore-server,JonAbrams/underscore,Joanna913/underscore,Gimcrack/underscore,Feiyang1/underscore,liyandalmllml/underscore,tnga/underscore-es,braddunbar/underscore,craigmichaelmartin/underscore,SeriaWei/underscore,hackreactor/underscore,jolthoff/underscore,polandeme/underscore,wxmfront/underscore,vincent1988/underscore,mairasala/underscore,thisismygithub/underscore,falqas/underscore,gougouGet/underscore,jpalomar/underscore,dxuehu/underscore,lis186/underscore,cintiamh/underscore,cgvarela/underscore,Tetpay/underscore,imsingh/underscore,mjhasbach/underscore,Feiyang1/underscore,sdwang/underscore,aziz-boudi4/underscore,liyandalmllml/underscore,liminghui/underscore,akre54/underscore,cnwhy/underscore,colemakdvorak/underscore,jiankers/underscore,appleboy/underscore,megawac/underscore,mitar/underscore,platinumazure/underscore,debutt/underscore,starterstep/underscore,JonAbrams/underscore,thiswildorchid/underscore,hackreactor/underscore,premkumargithub/underscore,thiswildorchid/underscore,nickkneafsey/underscore,elancom/underscore,keepgoingwm/underscore,zhangguangyong/underscore,oss6/underscore,akre54/underscore,singhsterabhi/underscore,kuychaco/underscore,wxmfront/underscore,premkumargithub/underscore,mjhasbach/underscore,LiskHQ/underscore,natac13/underscore,dimitriwalters/underscore,mitar/underscore,mairasala/underscore,documentcloud/underscore,veg/underscore,dxuehu/underscore,jpalomar/underscore,roychen-7/underscore,Gimcrack/underscore,singhsterabhi/underscore,ijidan/underscore,PengShi-sp/underscore,WangRex/underscore,bkillenit/underscore,keepgoingwm/underscore,huangnan1/2016gitStudy,ryanwholey/underscore,PUSEN/underscore,RepmujNetsik/underscore,prosenjit-itobuz/underscore,componentizr/underscore,emiel187/underscore,1800joe/underscore,vincent1988/underscore,xiaoqiang730730/underscore,bkillenit/underscore,kanso/underscore,beenlee/underscore,Joanna913/underscore,jiankers/underscore,youprofit/underscore,cailong1028/underscore,rlugojr/underscore,ElseZhang/underscore,zabefloyd/underscore,platinumazure/underscore,snackshen/underscore,jordanwink201/underscore,huangnan1/2016gitStudy,ligson/underscore,Forever8/underscore,kanso/underscore,Tim-Zhang/underscore,AaronNGray/underscore-server,prosenjit-itobuz/underscore,jridgewell/underscore,paulfalgout/underscore,liminghui/underscore,strongconjunctions/underscore,ElseZhang/underscore,LiskHQ/underscore,cgvarela/underscore,oss6/underscore,lqjack/underscore,natac13/underscore,huzion/underscore,Yangani/underscore,greyhwndz/underscore,imsingh/underscore,kwangkim/underscore,amdjs/underscore,RepmujNetsik/underscore,jonot/underscore,kairyan/underscore,jashkenas/underscore,craigmichaelmartin/underscore,sdwang/underscore,snackshen/underscore,kwangkim/underscore,zabefloyd/underscore,SeriaWei/underscore,yekg880809/underscore,aziz-boudi4/underscore,elancom/underscore,lqjack/underscore,ThiagoGarciaAlves/underscore,yekg880809/underscore