Google has resolved the issue and we're seeing jobs executing as expected. Please email support@travis-ci.com if you continue to see any network issues. Thanks for your patience during this issue.
Our cloud provider for sudo enabled builds, Google Compute Engine (GCE) is currently experiencing network connectivity issues and this affecting public and private builds. We're monitoring their status incident, https://status.cloud.google.com/incident/compute/17006, closely and will provide updates as we get them. During this incident you'll see failures connectivity to external resources like Launchpad PPAs, PyPI, RubyGems, etc.