fix: Update syntax for Terraform 0.15 (#135)

modules/iam-assumable-roles-with-saml/outputs.tf

 #Admin
 output "admin_iam_role_arn" {
   description = "ARN of admin IAM role"
-  value       = element(concat(aws_iam_role.admin.*.arn, list("")), 0)
+  value       = element(concat(aws_iam_role.admin.*.arn, [""]), 0)
 }
 
 output "admin_iam_role_name" {
   description = "Name of admin IAM role"
-  value       = element(concat(aws_iam_role.admin.*.name, list("")), 0)
+  value       = element(concat(aws_iam_role.admin.*.name, [""]), 0)
 }
 
 output "admin_iam_role_path" {
   description = "Path of admin IAM role"
-  value       = element(concat(aws_iam_role.admin.*.path, list("")), 0)
+  value       = element(concat(aws_iam_role.admin.*.path, [""]), 0)
 }
 
 output "poweruser_iam_role_arn" {
   description = "ARN of poweruser IAM role"
-  value       = element(concat(aws_iam_role.poweruser.*.arn, list("")), 0)
+  value       = element(concat(aws_iam_role.poweruser.*.arn, [""]), 0)
 }
 
 output "poweruser_iam_role_name" {
   description = "Name of poweruser IAM role"
-  value       = element(concat(aws_iam_role.poweruser.*.name, list("")), 0)
+  value       = element(concat(aws_iam_role.poweruser.*.name, [""]), 0)
 }
 
 output "poweruser_iam_role_path" {
   description = "Path of poweruser IAM role"
-  value       = element(concat(aws_iam_role.poweruser.*.path, list("")), 0)
+  value       = element(concat(aws_iam_role.poweruser.*.path, [""]), 0)
 }
 
 # Readonly
 output "readonly_iam_role_arn" {
   description = "ARN of readonly IAM role"
-  value       = element(concat(aws_iam_role.readonly.*.arn, list("")), 0)
+  value       = element(concat(aws_iam_role.readonly.*.arn, [""]), 0)
 }
 
 output "readonly_iam_role_name" {
   description = "Name of readonly IAM role"
-  value       = element(concat(aws_iam_role.readonly.*.name, list("")), 0)
+  value       = element(concat(aws_iam_role.readonly.*.name, [""]), 0)
 }
 
 output "readonly_iam_role_path" {
   description = "Path of readonly IAM role"
-  value       = element(concat(aws_iam_role.readonly.*.path, list("")), 0)
+  value       = element(concat(aws_iam_role.readonly.*.path, [""]), 0)
 }