Update prettier & fix parser warnings

[ismail-syed]

This PR fixes #3, and fixes #5.

As per this comment: deprecated postcss in favor of css.

Before

• using postcss, we see the warnings:
  

After

• with css, no warnings:
  

[codecov]

Codecov Report

Merging #6 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master       #6   +/-   ##
=======================================
  Coverage   98.03%   98.03%           
=======================================
  Files           2        2           
  Lines          51       51           
=======================================
  Hits           50       50           
  Misses          1        1

Impacted Files	Coverage Δ
src/index.js	98% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2e37e73...24afc99. Read the comment docs.

[lucasmotta]

@hugomrdias any chance you can look into this PR? Very simple change, but it removes a very annoying deprecation warning.

[paleite]

Would be awesome if we could get an update on this, @hugomrdias !

[mazhermon]

Keen for this also. Getting a lot of noise in the console even when using the --quiet flag. Thanks for the great package though :) Super keen for this patch to go in. Cheers

[isellsoap]

I created a temporary package containing these fixes: https://www.npmjs.com/package/prettier-stylelint-temp