Adjust options to prometheus 1.6

Change-Id: I30c3e71d3dd99df89bfd2729b75a3cfe7e4a58fb
diff --git a/docker/swarm/stack/monitoring.yml b/docker/swarm/stack/monitoring.yml
index 755b5d7..4371367 100644
--- a/docker/swarm/stack/monitoring.yml
+++ b/docker/swarm/stack/monitoring.yml
@@ -79,6 +79,5 @@
                 bind_address: ${prometheus:server:bind:address}
                 storage_local_engine: ${prometheus:server:storage:local:engine}
                 storage_local_retention: ${prometheus:server:storage:local:retention}
-                storage_local_memory_chunks: ${prometheus:server:storage:local:memory_chunks}
-                storage_local_max_chunks_to_persist: ${prometheus:server:storage:local:max_chunks_to_persist}
+                storage_local_target_heap_size: ${prometheus:server:storage:local:target_heap_size}
                 storage_local_num_fingerprint_mutexes: ${prometheus:server:storage:local:num_fingerprint_mutexes}