reinstall fixed it for me:
sudo apt-get remove elixir
sudo apt-get remove esl-erlang
sudo apt-get update
sudo apt-get install esl-erlang
sudo apt-get install elixir
after that I have a normal release and not an RC any more:
Erlang/OTP 20 [erts-9.0] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:10] [hipe] [kernel-poll:false]
somehow it was only doable with reinstall and not with update. My guess is RC made it there by mistake and we who updated to it were stuck with it
