As the hottest of the press features of GitHub Actions
requires using YAML rather than HCL.

While creating the `$ npm install` step in the
GitHub Actions workflow, I forgot to state the fact that
the `$ npm test` step "needs" the install deps step
to have successfully run first.

..forgot to install dependencies before executing
`$ npm test` which obviously exploded due to the
fact that `eslint` and friends weren't available.

As a means of seeing how GitHub Actions
work compared to Travis CI, these changes creates
a so-called workflow that runs `$ npm test`
upon every `$ git push` to the repository.