Fix the return value of riot.mount in doc
Fix the return value of riot.mount in doc

dp-lewis/riot,txchen/riotjs,scalabl3/riot,zawsx/js-lib-webcomponents-react-riot,seedtigo/riot,qrb/riotjs,mike-ward/riot,muut/riotjs,seedtigo/riot,stonexer/riot,duongphuhiep/riot,zawsx/js-lib-webcomponents-react-riot,scalabl3/riot,marcioj/riot,sylvainpolletvillard/riot,xtity/riot,tao-zeng/riot,crisward/riot,beni55/riot,rasata/riot,thepian/riot,beni55/riot,davidmarkclements/riot,muut/riotjs,thepian/riot,madlordory/riot,duongphuhiep/riot,rthbound/riot,xtity/riot,mike-ward/riot,laomu1988/riot,txchen/riotjs,daemonchen/riotjs,madlordory/riot,qrb/riotjs,dschnare/riot,joshcartme/riot,rthbound/riot,AndrewSwerlick/riot,rasata/riot,baysao/riot,AndrewSwerlick/riot,crisward/riot,joshcartme/riot,baysao/riot,dschnare/riot,noodle-learns-programming/riot,sylvainpolletvillard/riot,chetanism/riot,chetanism/riot,tao-zeng/riot,dp-lewis/riot,noodle-learns-programming/riot,laomu1988/riot,davidmarkclements/riot,stonexer/riot,daemonchen/riotjs,marcioj/riot