Improvement: Require kubernetes provider >=1.11.1 (#784)

BREAKING CHANGE: The terraform-aws-eks module now require at least kubernetes `1.11.1`. This may cause terraform to fail to init if users have set version = "1.10" like we had in the examples.

versions.tf

@@ -7,6 +7,6 @@ terraform {
     null       = ">= 2.1"
     template   = ">= 2.1"
     random     = ">= 2.1"
-    kubernetes = ">= 1.6.2"
+    kubernetes = ">= 1.11.1"
   }
 }