Only apply forin check to for…in loops.
Only apply forin check to for…in loops.

This change corrects the behaviour of JSHint’s forin option
on for…of loops; the two share many checks, but this:

    for (var x of [1, 2, 3]) {
        // …
    }

should not result in the warning reported by jshint/jshint#1079:

> The body of a for in should be wrapped in an if statement to filter
> unwanted properties from the prototype.

crivas/jshint,lukeapage/jshint,scottsmeester/jshint,freeyiyi1993/jshint,louwers/jshint,llucbrell/jshint,elkingtonmcb/jshint,Jeremy017/jshint,Jeremy017/jshint,doggy8088/jshint,cnbin/jshint,beni55/jshint,ecomfe/edp-jshint,jonnyreeves/jshint,aisk/jshint,scottsmeester/jshint,gameclosure/jsiohint,shreyasgaonkar/jshint,n8io/jshint,paul-wade/jshint,aisk/jshint,louwers/jshint,n8io/jshint,jshint/jshint,fashionsun/jshint,max789/jshint,darongE/jshint,behind2/jshint,marian-r/jshint,gloryknight/jshint,luisbrito/jshint,wzup/jshint,gtanner/jshint,jagdeesh109/jshint,elkingtonmcb/jshint,gtanner/jshint,davidjb/jshint,mohsen1/jshint,ljharb/jshint,doggy8088/jshint,cnbin/jshint,jagdeesh109/jshint,jugglinmike/jshint,Endika/jshint,lukeapage/jshint,mohsen1/jshint,kidaa/jshint,niedzielski/jshint,fashionsun/jshint,mcanthony/jshint,yadimon/jshint,laurensortiz/jshint,rwaldron/jshint,supriyantomaftuh/jshint,ljharb/jshint,luisbrito/jshint,silverwind/jshint,llucbrell/jshint,Joy603/jshint,laurensortiz/jshint,paul-wade/jshint,mrjoelkemp/jshint,nitinlal/jshint,wisavalite/jshint,kidaa/jshint,wzup/jshint,pansay/jshint,wisavalite/jshint,shreyasgaonkar/jshint,paladox/jshint,jugglinmike/jshint,paragag/AntiRedis,alivesay/jshint,max789/jshint,lovemeblender/jshint,stevemao/jshint,Joy603/jshint,BridgeAR/jshint,yyx990803/jshint,ThiagoGarciaAlves/jshint,zynick/jshint,Endika/jshint,supriyantomaftuh/jshint,thomas658/jshint,nicolo-ribaudo/jshint,davidjb/jshint,freeyiyi1993/jshint,mrjoelkemp/jshint,kangax/jshint,meh-uk/jshint,nitinlal/jshint,alivesay/jshint,marian-r/jshint,yadimon/jshint,niedzielski/jshint,pansay/jshint,beni55/jshint,stevemao/jshint,thomas658/jshint,BridgeAR/jshint,nicolo-ribaudo/jshint,crivas/jshint,AndriiGro/jshint,behind2/jshint,AndriiGro/jshint,mcanthony/jshint,jshint/jshint