Fix tests and activate linting for CI

[srenatus]

...such that this doesn't fire. Fixes #19.

[chris-rock]

@srenatus Why does it fire an exit_status?

[srenatus]

@chris-rock If runner.run doesn't return 0, an exception will be raised at the end of verifier.call() because the mock doesn't return anything unless told explicitly:

exit_code = runner.run
raise ActionFailed, "Inspec Runner returns #{exit_code}" unless exit_code == 0

This was added recently, I'm just adapting the tests.

[chris-rock]

• added inspec ruby styling
• fixed lint errors
• activated lint as default rake task

[arlimus]

This is a huge quality improvement, wow!! Excellent 🎊 @srenatus and @chris-rock 👍