Fix: kafka image in docker-compose demo (#380)

Author: zth9

demo/docker-compose.yaml

@@ -68,7 +68,7 @@ services:
 
   kafka:
     container_name: kafka
-    image: confluentinc/cp-kafka
+    image: confluentinc/cp-kafka:7.2.15
     expose:
       - 9092
       - 9094