Kafka Docker image the HEAP_OPTS variable is not used

In the file 

https://github.com/debezium/docker-images/blob/7f26d70603711761898220f54ffa89d2b8eb5df1/kafka/1.5/docker-entrypoint.sh#L22

After checking the value of  `HEAP_OPTS` inside the sed the value `HEAP_OPTS` but it is mentioned incorrectly as `KAFKA_HEAP_OPTS`. 

It would be better if we want to keep to one variable either  `HEAP_OPTS` or `KAFKA_HEAP_OPTS`