build!: update library to use Node 12 (#835)
build!: update library to use Node 12 (#835)

* build!: update library to use Node 12
* build: fix broken Kokoro configuration test
* build: import version from package.json for tests
GoogleCloudPlatform/nodejs-docs-samples,GoogleCloudPlatform/nodejs-docs-samples,GoogleCloudPlatform/nodejs-docs-samples,GoogleCloudPlatform/nodejs-docs-samples