test(nodejs): remove 15 add 16 (#1322) (#909)

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -1,3 +1,3 @@
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest
-  digest: sha256:f092066de33d4a2a13ab13c8fa9dcb4f6b96fa1fb7d391bf19cd0c4921d997c0
+  digest: sha256:3563b6b264989c4f5aa31a3682e4df36c95756cfef275d3201508947cbfc511e

.github/workflows/ci.yaml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node: [10, 12, 14, 15]
+        node: [10, 12, 14, 16]
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v1