Development on the Google PHP client library moved to GitHub with the release of the 1.0.0-alpha, and now the 1.0 branch has reached beta status there will be no further releases of the 0.6 branch of the library.

Please take a look at the latest version on https://github.com/google/google-api-php-client

For information on migrating, please take a look at this guide: https://developers.google.com/api-client-library/php/guide/migration