Fix file validation for importer
Fix file validation for importer

refs #3339
- wrong call to file validation
- refs the issue because I get application/json on OSX? Is this
something Windows specific?

GarrethDottin/Habits-Design,patrickdbakke/ghost-spa,lukw00/Ghost,Sebastian1011/Ghost,jamesslock/Ghost,cwonrails/Ghost,veyo-care/Ghost,panezhang/Ghost,jiachenning/Ghost,edurangel/Ghost,leonli/ghost,arvidsvensson/Ghost,mattchupp/blog,SachaG/bjjbot-blog,wspandihai/Ghost,lethalbrains/Ghost,devleague/uber-hackathon,floofydoug/Ghost,uploadcare/uploadcare-ghost-demo,camilodelvasto/herokughost,smaty1/Ghost,rollokb/Ghost,klinker-apps/ghost,handcode7/Ghost,Dnlyc/Ghost,bitjson/Ghost,augbog/Ghost,delgermurun/Ghost,fredeerock/atlabghost,diancloud/Ghost,rito/Ghost,riyadhalnur/Ghost,cysys/ghost-openshift,telco2011/Ghost,novaugust/Ghost,codeincarnate/Ghost,GarrethDottin/Habits-Design,flomotlik/Ghost,SkynetInc/steam,ryansukale/ux.ryansukale.com,dYale/blog,dggr/Ghost-sr,davidmenger/nodejsfan,dylanchernick/ghostblog,UnbounDev/Ghost,ryansukale/ux.ryansukale.com,kaiqigong/Ghost,diogogmt/Ghost,r14r/fork_nodejs_ghost,k2byew/Ghost,morficus/Ghost,v3rt1go/Ghost,ladislas/ghost,rizkyario/Ghost,mikecastro26/ghost-custom,devleague/uber-hackathon,jiangjian-zh/Ghost,chevex/undoctrinate,edurangel/Ghost,skleung/blog,sfpgmr/Ghost,Kaenn/Ghost,daimaqiao/Ghost-Bridge,dYale/blog,chris-yoon90/Ghost,anijap/PhotoGhost,dymx101/Ghost,jin/Ghost,rchrd2/Ghost,mtvillwock/Ghost,RoopaS/demo-intern,JohnONolan/Ghost,lukaszklis/Ghost,jin/Ghost,PepijnSenders/whatsontheotherside,greyhwndz/Ghost,ASwitlyk/Ghost,nmukh/Ghost,denzelwamburu/denzel.xyz,obsoleted/Ghost,lowkeyfred/Ghost,bigertech/Ghost,ljhsai/Ghost,jaswilli/Ghost,exsodus3249/Ghost,ygbhf/Ghost,neynah/GhostSS,anijap/PhotoGhost,Klaudit/Ghost,k2byew/Ghost,Trendy/Ghost,Brunation11/Ghost,melissaroman/ghost-blog,carlosmtx/Ghost,vainglori0us/urban-fortnight,neynah/GhostSS,TribeMedia/Ghost,beautyOfProgram/Ghost,schneidmaster/theventriloquist.us,notno/Ghost,kwangkim/Ghost,v3rt1go/Ghost,tyrikio/Ghost,mohanambati/Ghost,bbmepic/Ghost,bitjson/Ghost,patterncoder/patterncoder,tyrikio/Ghost,pollbox/ghostblog,jaswilli/Ghost,kortemy/Ghost,Rovak/Ghost,hoxoa/Ghost,jamesslock/Ghost,kmeurer/Ghost,NamedGod/Ghost,kevinansfield/Ghost,mhhf/ghost-latex,blankmaker/Ghost,InnoD-WebTier/hardboiled_ghost,karmakaze/Ghost,lukekhamilton/Ghost,obsoleted/Ghost,dggr/Ghost-sr,STANAPO/Ghost,camilodelvasto/herokughost,Feitianyuan/Ghost,sifatsultan/js-ghost,ITJesse/Ghost-zh,darvelo/Ghost,nakamuraapp/new-ghost,sangcu/Ghost,situkangsayur/Ghost,mnitchie/Ghost,AlexKVal/Ghost,makapen/Ghost,skmezanul/Ghost,ineitzke/Ghost,julianromera/Ghost,RufusMbugua/TheoryOfACoder,krahman/Ghost,nmukh/Ghost,e10/Ghost,zeropaper/Ghost,JonathanZWhite/Ghost,aroneiermann/GhostJade,NikolaiIvanov/Ghost,notno/Ghost,adam-paterson/blog,ananthhh/Ghost,kaiqigong/Ghost,atandon/Ghost,katrotz/blog.katrotz.space,augbog/Ghost,PDXIII/Ghost-FormMailer,andrewconnell/Ghost,ladislas/ghost,ClarkGH/Ghost,Japh/Ghost,barbastan/Ghost,shrimpy/Ghost,ghostchina/Ghost-zh,ManRueda/manrueda-blog,johnnymitch/Ghost,SkynetInc/steam,gleneivey/Ghost,dai-shi/Ghost,uploadcare/uploadcare-ghost-demo,duyetdev/islab,zumobi/Ghost,etanxing/Ghost,imjerrybao/Ghost,blankmaker/Ghost,bastianbin/Ghost,Bunk/Ghost,edsadr/Ghost,ljhsai/Ghost,sifatsultan/js-ghost,mayconxhh/Ghost,Yarov/yarov,Azzurrio/Ghost,singular78/Ghost,daihuaye/Ghost,AnthonyCorrado/Ghost,pollbox/ghostblog,wallmarkets/Ghost,psychobunny/Ghost,lowkeyfred/Ghost,acburdine/Ghost,vainglori0us/urban-fortnight,yundt/seisenpenji,BlueHatbRit/Ghost,cobbspur/Ghost,kolorahl/Ghost,jaguerra/Ghost,camilodelvasto/localghost,sergeylukin/Ghost,sergeylukin/Ghost,laispace/laiblog,jparyani/GhostSS,ckousik/Ghost,influitive/crafters,UsmanJ/Ghost,manishchhabra/Ghost,rmoorman/Ghost,smedrano/Ghost,daimaqiao/Ghost-Bridge,wemakeweb/Ghost,liftup/ghost,allspiritseve/mindlikewater,lukekhamilton/Ghost,LeandroNascimento/Ghost,imjerrybao/Ghost,novaugust/Ghost,Netazoic/bad-gateway,tidyui/Ghost,jiangjian-zh/Ghost,psychobunny/Ghost,Shauky/Ghost,stridespace/Ghost,xiongjungit/Ghost,dbalders/Ghost,leonli/ghost,Jai-Chaudhary/Ghost,ErisDS/Ghost,thomasalrin/Ghost,Dnlyc/Ghost,daimaqiao/Ghost-Bridge,leonli/ghost,aschmoe/jesse-ghost-app,NamedGod/Ghost,IbrahimAmin/Ghost,mhhf/ghost-latex,dqj/Ghost,daihuaye/Ghost,ygbhf/Ghost,shannonshsu/Ghost,hilerchyn/Ghost,liftup/ghost,sajmoon/Ghost,ghostchina/Ghost.zh,yangli1990/Ghost,r1N0Xmk2/Ghost,jacostag/Ghost,optikalefx/Ghost,jomofrodo/ccb-ghost,smedrano/Ghost,edsadr/Ghost,davidmenger/nodejsfan,zackslash/Ghost,tadityar/Ghost,cqricky/Ghost,lanffy/Ghost,mtvillwock/Ghost,claudiordgz/Ghost,theonlypat/Ghost,hnarayanan/narayanan.co,vainglori0us/urban-fortnight,hilerchyn/Ghost,BlueHatbRit/Ghost,etanxing/Ghost,VillainyStudios/Ghost,MadeOnMars/Ghost,ManRueda/Ghost,FredericBernardo/Ghost,cysys/ghost-openshift,kevinansfield/Ghost,lf2941270/Ghost,tandrewnichols/ghost,BayPhillips/Ghost,laispace/laiblog,lf2941270/Ghost,thomasalrin/Ghost,carlyledavis/Ghost,gabfssilva/Ghost,morficus/Ghost,VillainyStudios/Ghost,benstoltz/Ghost,PaulBGD/Ghost-Plus,beautyOfProgram/Ghost,Kikobeats/Ghost,jomofrodo/ccb-ghost,sfpgmr/Ghost,Alxandr/Blog,francisco-filho/Ghost,johnnymitch/Ghost,netputer/Ghost,cncodog/Ghost-zh-codog,katrotz/blog.katrotz.space,Romdeau/Ghost,cysys/ghost-openshift,johngeorgewright/blog.j-g-w.info,AlexKVal/Ghost,melissaroman/ghost-blog,ngosinafrica/SiteForNGOs,STANAPO/Ghost,janvt/Ghost,petersucks/blog,PepijnSenders/whatsontheotherside,flpms/ghost-ad,JonSmith/Ghost,ericbenson/GhostAzureSetup,memezilla/Ghost,NovaDevelopGroup/Academy,etdev/blog,jacostag/Ghost,PeterCxy/Ghost,davidenq/Ghost-Blog,Elektro1776/javaPress,Xibao-Lv/Ghost,kmeurer/Ghost,hnarayanan/narayanan.co,Polyrhythm/dolce,jgillich/Ghost,acburdine/Ghost,tmp-reg/Ghost,jeonghwan-kim/Ghost,veyo-care/Ghost,ignasbernotas/nullifer,bsansouci/Ghost,prosenjit-itobuz/Ghost,lethalbrains/Ghost,ananthhh/Ghost,stridespace/Ghost,tmp-reg/Ghost,devleague/uber-hackathon,ThorstenHans/Ghost,handcode7/Ghost,NovaDevelopGroup/Academy,cicorias/Ghost,metadevfoundation/Ghost,rizkyario/Ghost,javorszky/Ghost,tanbo800/Ghost,achimos/ghost_as,wspandihai/Ghost,tadityar/Ghost,yundt/seisenpenji,omaracrystal/Ghost,allanjsx/Ghost,rouanw/Ghost,sebgie/Ghost,ITJesse/Ghost-zh,ddeveloperr/Ghost,Elektro1776/javaPress,Japh/shortcoffee,djensen47/Ghost,Netazoic/bad-gateway,sebgie/Ghost,ashishapy/ghostpy,YY030913/Ghost,rameshponnada/Ghost,jparyani/GhostSS,RufusMbugua/TheoryOfACoder,Yarov/yarov,JulienBrks/Ghost,Aaron1992/Ghost,InnoD-WebTier/hardboiled_ghost,NovaDevelopGroup/Academy,thehogfather/Ghost,ASwitlyk/Ghost,ErisDS/Ghost,llv22/Ghost,laispace/laiblog,madole/diverse-learners,GroupxDev/javaPress,sankumsek/Ghost-ashram,rafaelstz/Ghost,ballPointPenguin/Ghost,mlabieniec/ghost-env,tksander/Ghost,trunk-studio/Ghost,riyadhalnur/Ghost,alecho/Ghost,letsjustfixit/Ghost,schematical/Ghost,woodyrew/Ghost,SachaG/bjjbot-blog,nneko/Ghost,dylanchernick/ghostblog,Bunk/Ghost,vishnuharidas/Ghost,woodyrew/Ghost,sceltoas/Ghost,cwonrails/Ghost,syaiful6/Ghost,rito/Ghost,novaugust/Ghost,Klaudit/Ghost,DesenTao/Ghost,gcamana/Ghost,wallmarkets/Ghost,mlabieniec/ghost-env,JohnONolan/Ghost,sajmoon/Ghost,tanbo800/Ghost,no1lov3sme/Ghost,zhiyishou/Ghost,fredeerock/atlabghost,Loyalsoldier/Ghost,mttschltz/ghostblog,akveo/akveo-blog,davidenq/Ghost-Blog,benstoltz/Ghost,bsansouci/Ghost,ErisDS/Ghost,IbrahimAmin/Ghost,diogogmt/Ghost,achimos/ghost_as,aschmoe/jesse-ghost-app,bisoe/Ghost,uniqname/everydaydelicious,ashishapy/ghostpy,zackslash/Ghost,syaiful6/Ghost,greenboxindonesia/Ghost,icowan/Ghost,KnowLoading/Ghost,Remchi/Ghost,freele/ghost,Jai-Chaudhary/Ghost,MadeOnMars/Ghost,Coding-House/Ghost,mlabieniec/ghost-env,JulienBrks/Ghost,JohnONolan/Ghost,scopevale/wethepeopleweb.org,axross/ghost,trunk-studio/Ghost,kevinansfield/Ghost,zeropaper/Ghost,metadevfoundation/Ghost,patterncoder/patterncoder,petersucks/blog,no1lov3sme/Ghost,tchapi/igneet-blog,acburdine/Ghost,carlosmtx/Ghost,disordinary/Ghost,PeterCxy/Ghost,rmoorman/Ghost,Loyalsoldier/Ghost,ignasbernotas/nullifer,ivantedja/ghost,ghostchina/website,zhiyishou/Ghost,pathayes/FoodBlog,vloom/blog,r14r/fork_nodejs_ghost,katiefenn/Ghost,wangjun/Ghost,karmakaze/Ghost,Remchi/Ghost,vloom/blog,madole/diverse-learners,jorgegilmoreira/ghost,Romdeau/Ghost,andrewconnell/Ghost,influitive/crafters,neynah/GhostSS,nneko/Ghost,dbalders/Ghost,zumobi/Ghost,cncodog/Ghost-zh-codog,Feitianyuan/Ghost,darvelo/Ghost,BayPhillips/Ghost,alexandrachifor/Ghost,GroupxDev/javaPress,pensierinmusica/Ghost,Japh/Ghost,duyetdev/islab,bosung90/Ghost,telco2011/Ghost,pbevin/Ghost,chris-yoon90/Ghost,ryanbrunner/crafters,dgem/Ghost,jorgegilmoreira/ghost,ClarkGH/Ghost,qdk0901/Ghost,ericbenson/GhostAzureSetup,epicmiller/pages,skmezanul/Ghost,lukaszklis/Ghost,thinq4yourself/Unmistakable-Blog,ManRueda/Ghost,javimolla/Ghost,bosung90/Ghost,smaty1/Ghost,rouanw/Ghost,makapen/Ghost,alecho/Ghost,Gargol/Ghost,kortemy/Ghost,singular78/Ghost,jomahoney/Ghost,hnq90/Ghost,shrimpy/Ghost,velimir0xff/Ghost,greyhwndz/Ghost,pathayes/FoodBlog,tandrewnichols/ghost,shannonshsu/Ghost,dggr/Ghost-sr,cwonrails/Ghost,yanntech/Ghost,yanntech/Ghost,llv22/Ghost,denzelwamburu/denzel.xyz,hoxoa/Ghost,jgladch/taskworksource,NikolaiIvanov/Ghost,schematical/Ghost,LeandroNascimento/Ghost,weareleka/blog,FredericBernardo/Ghost,leninhasda/Ghost,javimolla/Ghost,phillipalexander/Ghost,bisoe/Ghost,flpms/ghost-ad,sebgie/Ghost,djensen47/Ghost,mdbw/ghost,JonSmith/Ghost,ckousik/Ghost,wangjun/Ghost,dgem/Ghost,tuan/Ghost,UnbounDev/Ghost,adam-paterson/blog,dai-shi/Ghost,rizkyario/Ghost,camilodelvasto/localghost,cncodog/Ghost-zh-codog,mttschltz/ghostblog,Alxandr/Blog,TryGhost/Ghost,dbalders/Ghost,developer-prosenjit/Ghost,ddeveloperr/Ghost,jparyani/GhostSS,Coding-House/Ghost,ngosinafrica/SiteForNGOs,memezilla/Ghost,telco2011/Ghost,skleung/blog,pbevin/Ghost,Kikobeats/Ghost,ivanoats/ivanstorck.com,akveo/akveo-blog,ryanbrunner/crafters,francisco-filho/Ghost,Trendy/Ghost,atandon/Ghost,bastianbin/Ghost,mohanambati/Ghost,kmeurer/GhostAzureSetup,davidenq/Ghost-Blog,mayconxhh/Ghost,NodeJSBarenko/Ghost,tksander/Ghost,Japh/shortcoffee,mdbw/ghost,icowan/Ghost,AileenCGN/Ghost,klinker-apps/ghost,rameshponnada/Ghost,PDXIII/Ghost-FormMailer,diancloud/Ghost,virtuall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