fix: Fix interpolation in docker compose file, remove unnecessary version attribute

Author: tizoc

docker-compose.block-producer.yml

@@ -1,10 +1,8 @@
-version: '3.8'
-
 services:
   openmina-node:
     image: openmina/openmina:${OPENMINA_TAG:-latest}
     entrypoint: >
-      sh -c 'openmina node --producer-key /root/.openmina/producer-key ${COINBASE_RECEIVER:+--coinbase-receiver $COINBASE_RECEIVER}'
+      sh -c "openmina node --producer-key /root/.openmina/producer-key $${COINBASE_RECEIVER:+--coinbase-receiver $$COINBASE_RECEIVER}"
     ports:
       - "3000:3000"
     volumes: