Ubuntu Zesty (17.04) is EOL, upgrade to Artful (17.10). (#187)
Ubuntu Zesty (17.04) is EOL, upgrade to Artful (17.10). (#187)

The builds broke because Zesty became EOL on 2018-01-13.
googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp