Add basic tests + travis-ci

[transitive-bullshit]

• adds eslint tests
• adds prettier tests
• minor fixes to codebase to get tests to pass
• added travis-ci

This is the first of several PRs that will add some basic unit and integration tests.

[tobiaslins]

Thanks @transitive-bullshit !

Can you please fix the conflicts from the dependency update merge? that would be great! :)