Netlify configuration is outdated

[hishamhm]

Hi @darrenjennings! Could you take a look at the Netlify configuration enabled for this repo? I think you're the only one with access to it right now. It is currently failing for all PRs on this repo:

Example failure from one of the currently-open PRs:
https://app.netlify.com/sites/teal-playground/deploys/654713b2898b73000874bb4f

If you click on "Initializing", you'll see this:

1:01:54 AM: ---------------------------------------------------------------------
  UNSUPPORTED BUILD IMAGE

  The build image for this site uses Ubuntu 16.04 Xenial Xerus, which is no longer supported.

  To enable builds for this site, select a later build image at the following link:
  https://app.netlify.com/sites/teal-playground/settings/deploys#build-image-selection

  For more details, visit the build migration guide:
  https://answers.netlify.com/t/please-read-end-of-support-for-xenial-build-image-everything-you-need-to-know/68239
  ---------------------------------------------------------------------

I expect it to be a matter of tweaking the Netlify configuration on your end without any code changes, since nothing we do is distro-specific, could you take a look? (I currently have Teal Playground builds working without issues on the https://github.com/teal-playground/tl repo using a different Netlify deploy associated to my own account.)