Added NPM version badge to the README
Added NPM version badge to the README

From author's email: "The badge helps your followers easily discover the NPM module associated with your Github repo.  I was wondering if you'd be interested in using this for JSHint."
alivesay/jshint,ljharb/jshint,paul-wade/jshint,luisbrito/jshint,mcanthony/jshint,gloryknight/jshint,alivesay/jshint,aisk/jshint,laurensortiz/jshint,raix/jshint,shreyasgaonkar/jshint,nitinlal/jshint,yyx990803/jshint,zynick/jshint,doggy8088/jshint,ecomfe/edp-jshint,wisavalite/jshint,scottsmeester/jshint,elkingtonmcb/jshint,elkingtonmcb/jshint,lukeapage/jshint,jshint/jshint,mohsen1/jshint,behind2/jshint,paragag/AntiRedis,yadimon/jshint,nitinlal/jshint,nicolo-ribaudo/jshint,louwers/jshint,n8io/jshint,jshint/jshint,wzup/jshint,kangax/jshint,louwers/jshint,marian-r/jshint,marian-r/jshint,cnbin/jshint,beni55/jshint,thomas658/jshint,fashionsun/jshint,meh-uk/jshint,gtanner/jshint,mohsen1/jshint,pansay/jshint,fashionsun/jshint,scottsmeester/jshint,gameclosure/jsiohint,max789/jshint,jagdeesh109/jshint,cnbin/jshint,darongE/jshint,BridgeAR/jshint,AndriiGro/jshint,freeyiyi1993/jshint,rwaldron/jshint,nicolo-ribaudo/jshint,Endika/jshint,pansay/jshint,fairfieldt/jshint,niedzielski/jshint,luisbrito/jshint,llucbrell/jshint,mcanthony/jshint,paladox/jshint,kidaa/jshint,max789/jshint,wisavalite/jshint,shreyasgaonkar/jshint,n8io/jshint,Khan/jshint,niedzielski/jshint,lukeapage/jshint,lovemeblender/jshint,thomas658/jshint,beni55/jshint,mrjoelkemp/jshint,davidjb/jshint,supriyantomaftuh/jshint,ljharb/jshint,wzup/jshint,stevemao/jshint,kidaa/jshint,laurensortiz/jshint,freeyiyi1993/jshint,stevemao/jshint,jugglinmike/jshint,jugglinmike/jshint,Jeremy017/jshint,Endika/jshint,behind2/jshint,ThiagoGarciaAlves/jshint,yadimon/jshint,ghtest712/bearded-octo-dangerzone,llucbrell/jshint,SqrTT/dwhint,silverwind/jshint,Jeremy017/jshint,crivas/jshint,gtanner/jshint,aisk/jshint,supriyantomaftuh/jshint,crivas/jshint,jonnyreeves/jshint,jagdeesh109/jshint,Joy603/jshint,davidjb/jshint,doggy8088/jshint,BridgeAR/jshint,AndriiGro/jshint,paul-wade/jshint,mrjoelkemp/jshint,Joy603/jshint