Update syntax to work with modern Terraform (#26)

* provider blocks and versions

* skip the weird adding an empty list and then compacting, just use the variables directly

* require terraform version 0.13 or greater

loader.tf

@@ -8,8 +8,8 @@ resource "aws_lambda_function" "loader" {
   timeout       = 900
 
   vpc_config {
-    subnet_ids         = compact(concat(var.lambda_loader_subnet_ids, list("")))
-    security_group_ids = compact(concat(var.lambda_loader_security_group_ids, list("")))
+    subnet_ids         = var.lambda_loader_subnet_ids
+    security_group_ids = var.lambda_loader_security_group_ids
   }
 
   environment {

s3.tf

@@ -1,6 +1,5 @@
 # Additional provider configuration for region your controlshift platform lives within.
 provider "aws" {
-  version = "~> 2.0"
   alias  = "controlshift"
   region = var.controlshift_aws_region
 }

versions.tf

@@ -0,0 +1,21 @@
+terraform {
+  required_version = ">= 0.13"
+  required_providers {
+    archive = {
+      source = "hashicorp/archive"
+    }
+    aws = {
+      source = "hashicorp/aws"
+      version = "~> 2.0"
+    }
+    http = {
+      source = "hashicorp/http"
+    }
+    random = {
+      source = "hashicorp/random"
+    }
+    template = {
+      source = "hashicorp/template"
+    }
+  }
+}