ElastiCache: Set node_type as cache.t3.micro

Change to recomended node type.

* https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/CacheNodes.SupportedTypes.html

* https://aws.amazon.com/jp/elasticache/previous-generation/

* https://pc.watch.impress.co.jp/docs/column/ubiq/1461095.html

elasticache.tf

@@ -26,7 +26,7 @@ resource "aws_elasticache_cluster" "this" {
   cluster_id           = "${var.prefix}-elasticache-cluster-${var.environment}"
   engine               = "memcached"
   engine_version       = "1.6.22"
-  node_type            = "cache.t2.micro"
+  node_type            = "cache.t3.micro"
   num_cache_nodes      = 2
   parameter_group_name = "default.memcached1.6"
   port                 = 11211