change output syntax

Author: Nikita Dugar

outputs.tf

@@ -1,10 +1,7 @@
 # Module      : Redis
 # Description : Terraform module to create Elasticache Cluster and replica for Redis.
 output "id" {
-  value = var.cluster_enabled ? "" : concat(
-    aws_elasticache_replication_group.default.*.id,
-    aws_elasticache_replication_group.cluster.*.id
-  )[0]
+  value = var.cluster_enabled ? "" : (var.replication_enabled ? join("", aws_elasticache_replication_group.default.*.id) : join("", aws_elasticache_replication_group.cluster.*.id))
   description = "Redis cluster id."
 }