Add CSS linting

[guillaumevincent]

Install ruby scss-lint package. Use the same mechanism as bootstrap.

Fixes https://patternfly.atlassian.net/browse/PTNFLY-2422

[andresgalante]

Thanks a lot @guillaumevincent ! I'll test it today

[guillaumevincent]

I started small, and will tackle one feature at a time I think travis is not enable right?

The current test (npm test) will raise an error because of the errors in sources/scss/*.scss

[andresgalante]

@bleathem this one works for me, can you please review it?

@guillaumevincent thanks a lot, I love it!

[andresgalante]

@guillaumevincent sorry that it took me so long to loop back to this. Bootstrap 4 beta 2 changed to stylelint and I think it's a good move. What do you think? should we follow it and merge a linter here?

thanks a lot!

[guillaumevincent]

let me update the pull request @andresgalante

[guillaumevincent]

Pull request update, I use stylelint now