fix docker tag for nats controller (#700)

.travis.yml

@@ -194,7 +194,7 @@ after_success:
       docker tag $CONTROLLER_IMAGE ${CONTROLLER_IMAGE_NAME}:latest
       docker tag $BUILDER_IMAGE ${BUILDER_IMAGE_NAME}:latest
       docker tag $KAFKA_CONTROLLER_IMAGE ${KAFKA_CONTROLLER_IMAGE_NAME}:latest
-      docker tag $NATS_CONTROLLER_IMAGE ${NATS_CONTROLLER_IMAGE}:latest
+      docker tag $NATS_CONTROLLER_IMAGE ${NATS_CONTROLLER_IMAGE_NAME}:latest
       docker push ${CONTROLLER_IMAGE_NAME}:latest
       docker push ${BUILDER_IMAGE_NAME}:latest
       docker push ${KAFKA_CONTROLLER_IMAGE_NAME}:latest