Update to node16 (#293)

Node 12 has an end of life on April 30, 2022.

This PR updates the default runtime to [node16](https://github.blog/changelog/2021-12-10-github-actions-github-hosted-runners-now-run-node-js-16-by-default/), rather then node12. 

This is supported on all Actions Runners v2.285.0 or later.

action.yml

@@ -24,5 +24,5 @@ inputs:
       Minimum 1 day.
       Maximum 90 days unless changed from the repository settings page.
 runs:
-  using: 'node12'
+  using: 'node16'
   main: 'dist/index.js'