test(nodejs): remove 15 add 16 (#1322) (#198)

Author: gcf-owl-bot[bot]

core/precise-date/.github/.OwlBot.lock.yaml

@@ -1,3 +1,3 @@
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest
-  digest: sha256:ba3f2990fefe465f89834e4c46f847ddb141afa54daa6a1d462928fa679ed143
+  digest: sha256:3563b6b264989c4f5aa31a3682e4df36c95756cfef275d3201508947cbfc511e