Cleaning up error output of cli on linting fail

[ben-ryder]

PR implementing the suggestion in #42 to switch from throwing an error to using process.exit(1) on linting failure .

This change should help make the output look clearer:

I also quickly merged your feature/add-e2e branch into a test branch and becuase the exit code is still the same, it looks like the tests still pass ok:

Fixes #42

[ben-ryder]

Hello, in retrospect I realize I've raised this PR out of nowhere as a new contributor, so I thought I'd come back and add a little context.

I was trying out the package and found myself wanting the same error output improvements detailed in the linked issue.
I thought I'd have a go implementing the suggestion myself and as it's worked well for me so far, thought I'd PR it back for consideration.

I'm happy to make any changes if you want, and would also understand if you don't want to edit this particular behavior. I also realize I've made an assumption about breaking changes in the commit message which I probably shouldn't have done as a random contributor, so I'm happy to force push a new commit message if you want too.

[barzik]

Hey @Ben-Ryder ! Thanks for this PR - I will push it in the next version.

[euclidesdry]

Hi, @barzik!

I've found your package, an incredible handful tool, and if you get a little time to push it (this PR) to the next version we'll be very thankful.

[AHaliq]

any updates on when this will merge or the next version release? @barzik

[vaidik]

This PR will be incredibly helpful as well. It'd be great to get this merged.