build!: update library to use Node 12 (#556)
build!: update library to use Node 12 (#556)

* build!: Update library to use Node 12

Co-authored-by: Owl Bot <7f39581e9a7ddb69f3fa3e6fc69a582ea2916fc9@users.noreply.github.com>
GoogleCloudPlatform/nodejs-docs-samples,GoogleCloudPlatform/nodejs-docs-samples,GoogleCloudPlatform/nodejs-docs-samples,GoogleCloudPlatform/nodejs-docs-samples