Use heartbeats in demo_relay.
Use heartbeats in demo_relay.

fkarb/pika-python3,knowsis/pika,reddec/pika,pika/pika,Zephor5/pika,jstnlef/pika,Tarsbot/pika,vitaly-krugl/pika,shinji-s/pika,vrtsystems/pika,renshawbay/pika-python3,hugoxia/pika,skftn/pika,zixiliuyue/pika,benjamin9999/pika