change output syntax

Author: Nikita Dugar

outputs.tf

@@ -2,9 +2,7 @@
 #Description : This terraform module creates set of Security Group and Security Group Rules
 #              resources in various combinations.
 output "security_group_ids" {
-  value = concat(
-    aws_security_group.default.*.id
-  )[0]
+  value = join("", aws_security_group.default.*.id)
   description = "IDs on the AWS Security Groups associated with the instance."
 }