fix travis config to _actually_ use containerzed infra

[squarebracket]

Description

When I was testing how to get the tests running in the dockerized travis infra, I was running in the travis docker image as root. When moving to the actual travis config, it told me I needed to be root, so without thinking I added sudo to the front. I was sure they'd allow package installs, which they do, but only using the apt addon; having sudo in the script would automatically kick you over to the VM-based infra.

Until they broke that yesterday.

Anyway, now we'll actually be using the containerized infra.

Requirements Checklist

• [x] Feature implemented / Bug fixed
• [ ] If necessary, more likely in a feature request than a bug fix
  • [ ] Unit Tests updated or fixed
  • [ ] Docs/guides updated
  • [ ] Example created (starter template on JSBin)
• [ ] Reviewed by Two Core Contributors

[squarebracket]

Travis is switching to all non-containerized infra, so this PR is no longer relevant.