Relax terraform-provider-ct version constraint

* Allow updating terraform-provider-ct to any release
beyond v0.3.2, but below v1.0. This relaxes the prior
constraint that allowed only v0.3.y provider versions

digital-ocean/container-linux/kubernetes/versions.tf

@@ -4,7 +4,7 @@ terraform {
   required_version = "~> 0.12.0"
   required_providers {
     digitalocean = "~> 1.3"
-    ct           = "~> 0.3.2"
+    ct           = "~> 0.3"
     template     = "~> 2.1"
     null         = "~> 2.1"
   }