Making terraform have no warnings

terraform/main.tf

@@ -1,6 +1,6 @@
 provider "aws" {
-  access_key = "${var.aws_access_key_id}"
-  secret_key = "${var.aws_secret_access_key}"
+  access_key = var.aws_access_key_id
+  secret_key = var.aws_secret_access_key
   region = "us-east-1"
 }
 
@@ -18,15 +18,15 @@ resource "aws_ses_receipt_rule_set" "main" {
 }
 
 resource "aws_ses_receipt_rule" "store" {
-  depends_on = ["aws_ses_receipt_rule_set.main"]
+  depends_on = [aws_ses_receipt_rule_set.main]
   name          = "store-${var.stage}"
   rule_set_name = "default-rule-set"
-  recipients    = ["${var.invoice_address}"]
+  recipients    = [var.invoice_address]
   enabled       = true
   scan_enabled  = true
 
   s3_action {
-    bucket_name = "${aws_s3_bucket.invoices.id}"
+    bucket_name = aws_s3_bucket.invoices.id
     position = "1"
   }
 }
@@ -133,10 +133,10 @@ POLICY
 }
 
 resource "aws_s3_bucket_notification" "mail_bucket_notification" {
-  bucket = "${aws_s3_bucket.invoices.id}"
+  bucket = aws_s3_bucket.invoices.id
 
   queue {
-    queue_arn     = "${aws_sqs_queue.integreat-mail.arn}"
+    queue_arn     = aws_sqs_queue.integreat-mail.arn
     events        = ["s3:ObjectCreated:*"]
     filter_suffix = ""
   }
@@ -147,21 +147,21 @@ resource "aws_iam_user" "app_user" {
 }
 
 resource "aws_iam_access_key" "app_user" {
-  user    = "${aws_iam_user.app_user.name}"
+  user    = aws_iam_user.app_user.name
 }
 
 resource "aws_iam_user_policy_attachment" "app_user_policy" {
-    user       = "${aws_iam_user.app_user.name}"
+    user       = aws_iam_user.app_user.name
     policy_arn = "arn:aws:iam::aws:policy/AdministratorAccess"
 }
 
 output "aws_access_key_id" {
-  value = "${aws_iam_access_key.app_user.id}"
+  value = aws_iam_access_key.app_user.id
   sensitive = true
 }
 
 output "aws_secret_access_key" {
-  value = "${aws_iam_access_key.app_user.secret}"
+  value = aws_iam_access_key.app_user.secret
   sensitive = true
 }
 
@@ -170,5 +170,5 @@ output "aws_default_region" {
 }
 
 output "queue_url" {
-  value = "${aws_sqs_queue.integreat-mail.id}"
+  value = aws_sqs_queue.integreat-mail.id
 }