Add support for stylelint extends (in the styelintrc)

[mehcode]

For instance (in stylelintrc):

{
  "extends": "stylelint-config-standard"
}

What happens now:

TypeError: Cannot read property 'indentation' of undefined
    at getIndentationFromStylelintConfig (.../node_modules/stylefmt/lib/params.js:43:26)
    at .../node_modules/stylefmt/lib/params.js:71:28

[bahmutov]

same problem, but great tools - I started using the stylefmt + stylelint combination, just like using standard + standard-format for my JS code. Great job!

[matype]

@mehcode @bahmutov Just released v3.3.0 to support stylelint extends, please update and confirm it :)

@seka Thank you for your work, bro!