Merge pull request #59 from trussworks/mk-pin-aws-3-0

Restrict to 3.x of the aws provider in anticipation of breaking changes

versions.tf

@@ -2,6 +2,6 @@ terraform {
   required_version = ">= 0.13.0"
 
   required_providers {
-    aws = ">= 3.0"
+    aws = ">= 3.0, < 4.0"
   }
 }