Update quickstart.md
Update quickstart.md

Correct sample code mistake.
heynickc/akka.net,Silv3rcircl3/akka.net,heynickc/akka.net,Silv3rcircl3/akka.net,simonlaroche/akka.net,simonlaroche/akka.net,amichel/akka.net,amichel/akka.net