basic example: correct elb tags (#458)

Added the "kubernetes.io/role/elb" tag to the public subnets in the
basic example.

Per documentation, ELB tag values are supposed to be "1". ELB tag values
being "true" are known not to work with aws-alb-ingress-controller.

https://docs.aws.amazon.com/eks/latest/userguide/load-balancing.html
https://docs.aws.amazon.com/eks/latest/userguide/alb-ingress.html

examples/basic/main.tf

@@ -101,11 +101,12 @@ module "vpc" {
 
   public_subnet_tags = {
     "kubernetes.io/cluster/${local.cluster_name}" = "shared"
+    "kubernetes.io/role/elb"                      = "1"
   }
 
   private_subnet_tags = {
     "kubernetes.io/cluster/${local.cluster_name}" = "shared"
-    "kubernetes.io/role/internal-elb"             = "true"
+    "kubernetes.io/role/internal-elb"             = "1"
   }
 }