Check the stylelint exit code before proceeding

[davidcornu]

Since the update to using JSON output, errors with stylelint have been hard to diagnose as the error message outputted relates to reviewdog's failure to parse the output rather than the error itself (see #116).

#114 likely doesn't help in this regard.

This PR checks the stylelint exit code and prints out its output if there was an error instead of passing the output to reviewdog.

[bert-mccutchen]

Love it. Looks like Stylelint's return code is dependent on if there are linter errors and not if the process itself failed. 😆

[davidcornu]

@bert-mccutchen it looks like the exit codes are documented here https://stylelint.io/user-guide/cli/#exit-codes

I'll update this PR to only continue if we see a 0 (everything fine) or 2 (lint error) code

[review-dog]

Hi, @davidcornu! We merged your PR to reviewdog! 🐶
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[github-actions]

🚀 [bumpr] Bumped! New version:v1.22.1 Changes:v1.22.0...v1.22.1