Switch CI to 3.5-stretch base image

[PeterJCLaw]

The jessie base images don't work for us now that jessie's deb repos have been archived.

[RealOrangeOne]

Is the only diff here meant to just be a newline?

[PeterJCLaw]

oops, no. not sure what happened there. It should have been a copy of sourcebots/robot-api#108. Will fix, probably via force-push so the commit messages make sense.

[kierdavis]

CI fails on a couple of linting errors, but those files aren't touched by this PR. My guess is that the linter has updated in the last 8 months since the last CI run and has gotten stricter. I'm fine if you want to merge this and create a new issue or PR to track the linting errors.

For future reference, if you push to a branch within this repository rather than in a fork, CircleCI will run on it and attach the results to the PR. It's done it here only because I copied your branch to this repository (under the name PeterJCLaw-update-ci). Shout if you don't have access to create branches on here.

[PeterJCLaw]

For future reference, if you push to a branch within this repository rather than in a fork, CircleCI will run on it and attach the results to the PR. It's done it here only because I copied your branch to this repository (under the name PeterJCLaw-update-ci). Shout if you don't have access to create branches on here.

Ah, we should definitely fix that as otherwise it makes it harder for people outside the org to contribute. There's a toggle in Circle which enables building PRs outside the main repo, I'll see if I can find it.

[PeterJCLaw]

For future reference, if you push to a branch within this repository rather than in a fork, CircleCI will run on it and attach the results to the PR. It's done it here only because I copied your branch to this repository (under the name PeterJCLaw-update-ci). Shout if you don't have access to create branches on here.

Ah, we should definitely fix that as otherwise it makes it harder for people outside the org to contribute. There's a toggle in Circle which enables building PRs outside the main repo, I'll see if I can find it.

I've now toggled this.

[kierdavis]

There's a toggle in Circle which enables building PRs outside the main repo

I wasn't aware that was a thing, but that's a better solution, thanks.