Require minimum Terraform and plugin versions

* Bump minimum Terraform version to v0.10.4
* Allow minor version updates for 1.0+ plugins
* Fix versions for plugins which are pre-1.0

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

@@ -0,0 +1,25 @@
+# Terraform version and plugin versions
+
+terraform {
+  required_version = ">= 0.10.4"
+}
+
+provider "digitalocean" {
+  version = "0.1.2"
+}
+
+provider "local" {
+  version = "~> 1.0.0"
+}
+
+provider "null" {
+  version = "~> 1.0.0"
+}
+
+provider "template" {
+  version = "~> 1.0.0"
+}
+
+provider "tls" {
+  version = "~> 1.0.0"
+}