With the introduction of a build step, where we take the source in .mjs
and build it into .js for non-ES Module systems, it's very important
that we remember to keep those two in sync.

That's what the CI job created in these changes ensure;

1. Run the build script
2. See if there are any pending git changes as a result

As long as there are no pending git changes, we're all fine and dandy,
or else we need to run the `npm run build` and commit the changes.

To ensure the ES module and source exposed by this package is compatible
with Deno going forward.

Added benefit is we get some sanity checks of the source code for free
due to Deno's built-in TypeScript compiler getting angry if it sees
things that does not make sense, in terms of missing function arguments
and so on.

This is a precursor to introducing a build step that will change what
we expose from this package. Better off writing some tests to verify
existing projects with different module systems continue to work as
expected.

This is a precursor to introducing a build step that will change what
we expose from this package. Better off writing some tests to verify
existing projects with different module systems continue to work as
expected.

Primarily because it's getting to be a pain in the backside to always
consider pre Node.js 6 when wanting to use up-to-date dependencies.

When initially creating the GitHub Actions
workflow, it was obviously forgotten to make
it also run on pull requests, not only when
changes are pushed to branches in the
original repository (not a fork).

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.