Update elb_service_account docs (#10299)

The current example using the ELB's account ID will trigger an update for a resource that uses the `.id` instead if the `.arn` syntax.

Once updated to the `.arn`, no changes are detected.

[ci skip]

website/source/docs/providers/aws/d/elb_service_account.html.markdown

@@ -32,7 +32,7 @@ resource "aws_s3_bucket" "elb_logs" {
       "Resource": "arn:aws:s3:::my-elb-tf-test-bucket/AWSLogs/*",
       "Principal": {
         "AWS": [
-          "${data.aws_elb_service_account.main.id}"
+          "${data.aws_elb_service_account.main.arn}"
         ]
       }
     }