make v6 as default ES version

packages/app/.env.development

@@ -14,7 +14,7 @@ MONGO_URI="mongodb://mongo:27017/growi"
 ELASTICSEARCH_URI="http://elasticsearch:9200/growi"
 ELASTICSEARCH_REQUEST_TIMEOUT=15000
 ELASTICSEARCH_REJECT_UNAUTHORIZED=false
-USE_ELASTICSEARCH_V6=false
+USE_ELASTICSEARCH_V6=true
 HACKMD_URI="http://localhost:3010"
 HACKMD_URI_FOR_SERVER="http://hackmd:3000"
 # DRAWIO_URI="http://localhost:8080/?offline=1&https=0"