Only test with hhvm on travis (#1369)
Only test with hhvm on travis (#1369)

* Only test with hhvm on travis

* Also remove build docs

googleapis/google-cloud-php,jdpedrie/google-cloud-php,chingor13/google-cloud-php,jdpedrie/google-cloud-php,chingor13/google-cloud-php,googleapis/google-cloud-php,chingor13/google-cloud-php,jdpedrie/google-cloud-php,googleapis/google-cloud-php