Fix auto scaling example to use ID rather than name

Lost a little while figuring out why this example wouldn't work, seems you need to use id, not name :)

examples/aws-asg/main.tf

@@ -47,7 +47,7 @@ resource "aws_launch_configuration" "web-lc" {
   image_id = "${lookup(var.aws_amis, var.aws_region)}"
   instance_type = "${var.instance_type}"
   # Security group
-  security_groups = ["${aws_security_group.default.name}"]
+  security_groups = ["${aws_security_group.default.id}"]
   user_data = "${file("userdata.sh")}"
   key_name = "${var.key_name}"
 }