Avoid churn around IAM policy (#15)

With the order as it was, Terraform Cloud would report a change to the policy, 
presumably because the list coming back from AWS was sorted unlike the HCL.

Author: jcf

main.tf

@@ -88,8 +88,8 @@ data "aws_iam_policy_document" "assume_role_policy_doc" {
       type = "Service"
 
       identifiers = [
-        "lambda.amazonaws.com",
         "edgelambda.amazonaws.com",
+        "lambda.amazonaws.com",
       ]
     }
   }