Update: default cluster_config

defaults

@@ -3,5 +3,5 @@
   "database": "oss://pgx-reference-data/annovar_hg38/",
   "hg": "hg38",
   "disk_size": "200",
-  "cluster_config": "OnDemand bcs.es.lc.4xlarge img-ubuntu-vpc"
+  "cluster_config": "OnDemand bcs.a2.3xlarge img-ubuntu-vpc"
 }