Cloud SQL Postgres sample requires user run a createTable.js script

[jsimonweb]

Issue: The Cloud SQL Postgres sample requires the user to first run a createTable.js script (in order to create the sample votes table) before running the sample itself.

Expected: Running the sample should create the sample table required to run the sample similarly to how the MySQL sample does it.

Sample location:
https://github.com/GoogleCloudPlatform/nodejs-docs-samples/tree/master/cloud-sql/postgres/knex