BigQuery: update quickstart to latest package versions.

[tswast]

Version 0.3.1 is the latest version of the google/cloud-bigquery package.

It includes some breaking changes, so the api samples will need to be updated separately.

[tswast]

#515 updates the "shakespeare" sample.

I started branch https://github.com/GoogleCloudPlatform/php-docs-samples/tree/bq-pkgs/bigquery/api for the other updates, but got a little stuck and moving on for now.

[tswast]

Build for PHP 5.6 fails with

+composer install -q
Your requirements could not be resolved to an installable set of packages.

The command "testing/run_all_tests.sh" exited with 1.

I don't know what to do about that.

[bshaffer]

It's probably because you ran composer install on a machine running a PHP version above 5.6, and so some dependencies are locked with versions that are only compatible with PHP > 5.6

[tswast]

Ah, yeah that's what I did. I was using PHP 7.2. Just pushed a commit after trying again with PHP 5.6.