Xenial build environment updates

The Ubuntu Xenial 16.04 build environment has been updated!

  • git now uses wire protocol version 2 to do its network operations, like git fetch or git clone
  • docker pulls from the GCE image cache where possible
  • PHP version aliases are now recognized

Aside from the highlights above, pre-installed languages and tools have also been updated. Here's the full list: https://docs.travis-ci.com/user/build-environment-updates/2019-04-11/

To use Xenial in your builds, make sure to specify dist: xenial in your .travis.yml file.

If you have any feedback, please, let us know in the community forum: Xenial. Thank you!