Changes extractSingle's return to call this._super
Changes extractSingle's return to call this._super

This makes the example in-line with the current documentation of DS.RESTSerializer.
I also was having trouble making extractSingle work in my application and making this change fixed it.
hibariya/data,jgwhite/data,topaxi/data,ryanpatrickcook/data,acburdine/data,stefanpenner/data,splattne/data,tstirrat/ember-data,sammcgrail/data,fpauser/data,gkaran/data,offirgolan/data,davidpett/data,minasmart/data,gniquil/data,whatthewhat/data,greyhwndz/data,Robdel12/data,jmurphyau/data,eriktrom/data,lostinpatterns/data,InboxHealth/data,funtusov/data,topaxi/data,slindberg/data,BookingSync/data,BBLN/data,EmberSherpa/data,bf4/data,duggiefresh/data,tarzan/data,lostinpatterns/data,webPapaya/data,swarmbox/data,danmcclain/data,HeroicEric/data,bcardarella/data,PrecisionNutrition/data,yaymukund/data,HeroicEric/data,H1D/data,k-fish/data,k-fish/data,workmanw/data,trisrael/em-data,greyhwndz/data,knownasilya/data,flowjzh/data,Kuzirashi/data,sammcgrail/data,nickiaconis/data,sebweaver/data,sammcgrail/data,wecc/data,pdud/data,arenoir/data,minasmart/data,andrejunges/data,faizaanshamsi/data,yaymukund/data,EmberSherpa/data,Addepar/ember-data,lostinpatterns/data,davidpett/data,Robdel12/data,Robdel12/data,kimroen/data,trisrael/em-data,intuitivepixel/data,fsmanuel/data,whatthewhat/data,gkaran/data,eriktrom/data,Addepar/ember-data,HeroicEric/data,davidpett/data,workmanw/data,courajs/data,dustinfarris/data,EmberSherpa/data,seanpdoyle/data,hibariya/data,Eric-Guo/data,sebweaver/data,bf4/data,sammcgrail/data,nickiaconis/data,zoeesilcock/data,hibariya/data,sebastianseilund/data,gabriel-letarte/data,Kuzirashi/data,martndemus/data,sebastianseilund/data,Turbo87/ember-data,topaxi/data,acburdine/data,ryanpatrickcook/data,arenoir/data,eriktrom/data,FinSync/ember-data,stefanpenner/data,PrecisionNutrition/data,Turbo87/ember-data,XrXr/data,stefanpenner/data,zoeesilcock/data,courajs/data,rtablada/data,andrejunges/data,Eric-Guo/data,InboxHealth/data,thaume/data,tarzan/data,Kuzirashi/data,swarmbox/data,rtablada/data,XrXr/data,H1D/data,k-fish/data,BookingSync/data,davidpett/data,in4mates/ember-data,yaymukund/data,kappiah/data,simaob/data,acburdine/data,knownasilya/data,topaxi/data,usecanvas/data,BookingSync/data,fsmanuel/data,in4mates/ember-data,mphasize/data,ryanpatrickcook/data,gniquil/data,swarmbox/data,sebweaver/data,mphasize/data,sebweaver/data,pdud/data,workmanw/data,Turbo87/ember-data,wecc/data,intuitivepixel/data,minasmart/data,k-fish/data,funtusov/data,tstirrat/ember-data,greyhwndz/data,lostinpatterns/data,fsmanuel/data,heathharrelson/data,simaob/data,sebastianseilund/data,greyhwndz/data,slindberg/data,offirgolan/data,Addepar/ember-data,vikram7/data,Robdel12/data,FinSync/ember-data,swarmbox/data,vikram7/data,fsmanuel/data,zoeesilcock/data,BBLN/data,tstirrat/ember-data,webPapaya/data,BBLN/data,pdud/data,jgwhite/data,flowjzh/data,gabriel-letarte/data,arenoir/data,tonywok/data,wecc/data,Turbo87/ember-data,trisrael/em-data,thaume/data,vikram7/data,eriktrom/data,BookingSync/data,rtablada/data,tonywok/data,vikram7/data,sebastianseilund/data,minasmart/data,funtusov/data,tstirrat/ember-data,PrecisionNutrition/data,flowjzh/data,wecc/data,faizaanshamsi/data,martndemus/data,seanpdoyle/data,tarzan/data,flowjzh/data,tonywok/data,rtablada/data,jgwhite/data,bcardarella/data,ryanpatrickcook/data,gabriel-letarte/data,splattne/data,heathharrelson/data,fpauser/data,tarzan/data,webPapaya/data,InboxHealth/data,slindberg/data,intuitivepixel/data,InboxHealth/data,bcardarella/data,faizaanshamsi/data,martndemus/data,danmcclain/data,stefanpenner/data,Eric-Guo/data,jgwhite/data,kappiah/data,EmberSherpa/data,gniquil/data,bf4/data,andrejunges/data,courajs/data,XrXr/data,heathharrelson/data,webPapaya/data,andrejunges/data,jmurphyau/data,HeroicEric/data,mphasize/data,gkaran/data,mphasize/data,danmcclain/data,nickiaconis/data,faizaanshamsi/data,simaob/data,tonywok/data,dustinfarris/data,zoeesilcock/data,usecanvas/data,heathharrelson/data,simaob/data,duggiefresh/data,kappiah/data,splattne/data,whatthewhat/data,nickiaconis/data,splattne/data,jmurphyau/data,PrecisionNutrition/data,bf4/data,arenoir/data,offirgolan/data,BBLN/data,funtusov/data,dustinfarris/data,XrXr/data,gkaran/data,usecanvas/data,acburdine/data,hibariya/data,duggiefresh/data,danmcclain/data,intuitivepixel/data,pdud/data,gniquil/data,kappiah/data,courajs/data,seanpdoyle/data,H1D/data,FinSync/ember-data,fpauser/data,kimroen/data,FinSync/ember-data,bcardarella/data,knownasilya/data,fpauser/data,whatthewhat/data,gabriel-letarte/data,dustinfarris/data,thaume/data,H1D/data,workmanw/data,Kuzirashi/data,usecanvas/data,duggiefresh/data,martndemus/data,thaume/data,in4mates/ember-data,Eric-Guo/data,jmurphyau/data,kimroen/data,offirgolan/data,yaymukund/data,seanpdoyle/data