Pin Erlang at 20.3 because the newest from ESL (21) does not work with RMQ
Pin Erlang at 20.3 because the newest from ESL (21) does not work with RMQ

(cherry picked from commit 03542ef616a2a849e8bfb0845427f50e741ea0c6)

pika/pika,vitaly-krugl/pika