support subscribe in gql 16 (#4)

* support subscribe

this import changed to `/subscribe` https://www.runpkg.com/?graphql@16.1.0/subscription/index.js

* change to subscription

import-map-overrides.json

···
   "executeSync": {
     "local": "executeSync",
     "from": "graphql"
+  },
+  "subscribe": {
+    "local": "subscribe",
+    "from": "graphql/subscription"
   }
 }