add a basic test setup

[mansona]

This is implemented in a similar way to what we did for broccoli-concat but I added a few extra older node versions since the travis file didn't define what versions we supported

I can't guarantee that this testing situation won't have some side-effects if we start to update other dependencies but since the main thing we want to release is just inlining code that was already in use I propose that we do the following:

• merge this PR
• setup release-plan and get a patch release shipped
• update whatever other dependencies are necessary to remove npm deprecations
• mark that dependency update PR as breaking and do a major release (optionally dropping older node versions)

There will likely be a need to remove some old node versions from testing anyway while upgrading deprecated packages so the conservative approach will likely be the right one 👍