Fix deprecation warning with IAM instance profile

Instance profiles can only be associated with a single role. Here, the `roles`
attribute of `aws_iam_instance_profile` was updated to `role`.

See: hashicorp/terraform#13130

main.tf

@@ -25,8 +25,8 @@ resource "aws_iam_role_policy_attachment" "ec2_service_role" {
 }
 
 resource "aws_iam_instance_profile" "container_instance" {
-  name  = "${aws_iam_role.container_instance_ec2.name}"
-  roles = ["${aws_iam_role.container_instance_ec2.name}"]
+  name = "${aws_iam_role.container_instance_ec2.name}"
+  role = "${aws_iam_role.container_instance_ec2.name}"
 }
 
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