Catch-up with linter-jshint

Copied and pasted the recent commits that happened in linter-jshint:

* Specify command as array: https://github.com/AtomLinter/linter-jshint/commit/bf0e64148d43016534683a9f4054b0ab462a85cf
* Infer type from match.{error,warning}: https://github.com/AtomLinter/linter-jshint/commit/9cfbe87313fd966da9fd68468359590e4a8a52be

This new version of the code does not seem to have regressions.