when un-forcing the height of the body, set it to an empty string.
when un-forcing the height of the body, set it to an empty string.

Until now we were setting the height to `auto`, but this would override
the height specifid inside a stylesheet. Setting it to an empty string
will reset the style property.

udhayam/skrollr,bspiritxp/skrollr,mumer92/skrollr,fengyiyi/skrollr,xiamiLi/skrollr,leendx/skrollr,divisionparzero/skrollr,NancyFan/skrollr,Kalmani/skrollr,boregan/skrollr,Bilyachenko/skrollr,kavallo/skrollr,2947721120/skrollr,Prinzhorn/skrollr,unxsist/skrollr,garylgh/skrollr,jianxiansining/skrollr,Kalmani/skrollr,AlphaStaxLLC/skrollr,Prinzhorn/skrollr,winglua/skrollr,bspiritxp/skrollr,VladimirGavrilov/skrollr,liqk2014/skrollr,utkarshx/skrollr,thenaughtychild/skrollr,2947721120/skrollr,piyushkhemka/skrollr,dshreyas11/skrollr,matthewgoodwin/skrollr,jianxiansining/skrollr,mikesoops/skrollr,dommuthu/skrollr,RohithKP/skrollr,garylgh/skrollr,AlphaStaxLLC/skrollr,dszls/skrollr,kavallo/skrollr,antoniocicerone/skrollr,mtgrunt/skrollr,mumer92/skrollr,alvarotrigo/skrollr,danieldietrich/skrollr,SanhNX/skrollr,VladimirGavrilov/skrollr,dommuthu/skrollr,unxsist/skrollr,matthewgoodwin/skrollr,fxck/skrollr,xiamiLi/skrollr,jeff235255/skrollr,cwj10/skrollr,leonardykris/skrollr,lauffenp/skrollr,RohithKP/skrollr,piyushkhemka/skrollr,alvarotrigo/skrollr,boregan/skrollr,utkarshx/skrollr,antoniocicerone/skrollr,SanhNX/skrollr,mikesoops/skrollr,grigorkh/skrollr,BenHeubl/skrollr,10by10pixel/skrollr,lauffenp/skrollr,GerHobbelt/skrollr,divisionparzero/skrollr,grigorkh/skrollr,udhayam/skrollr,GerHobbelt/skrollr,dshreyas11/skrollr,jeff235255/skrollr,thenaughtychild/skrollr,mtgrunt/skrollr,cwj10/skrollr,dszls/skrollr,10by10pixel/skrollr,danieldietrich/skrollr,NancyFan/skrollr,fxck/skrollr,leonardykris/skrollr,liqk2014/skrollr,winglua/skrollr,MassImpact/skrollr,MassImpact/skrollr,leendx/skrollr,fengyiyi/skrollr,Bilyachenko/skrollr,BenHeubl/skrollr