kafka version to be updated in bin/grid

SAMZA-565 updated Samza to use the new Kafka producer.
The downloaded package name provided for install() in install_kafka method is still pointing to the old kafka version. This leads to a file not found exception when you try to bootstrap or install kafka

mv: rename /Users/nramesh/.samza/download/kafka_2.10-0.8.1.1 to /Users/nramesh/Projects/samza-hello-samza/deploy/kafka: No such file or directory