new icon: postcss (original, plain, original-wordmark, plain-wordmark)

[canaleal]

Double check these details before you open a PR

• PR does not match another non-stale PR currently opened
• PR name matches the format new icon: Icon name (versions separated by comma). More details here
• PR's base is the develop branch.
• Your icons are inside a folder as seen here
• SVG matches the standards laid out here
• A new object is added in the devicon.json file as seen here

**This PR closes #1156 **

Link to prove your SVG is correct and up-to-date.

Official Website
https://postcss.org/

Github
https://github.com/postcss

Brand
https://github.com/postcss/brand

[github-actions]

Hi there,

I'm Devicons' Peek Bot and I just peeked at the icons that you wanted to add using icomoon.io.

Here are the SVGs as intepreted by Icomoon when we upload the files:

Here are the zoomed-in screenshots of the added icons as SVGs:

Here are the icons that will be generated by Icomoon:

Here are the zoomed-in screenshots of the added icons as icons:

Here are the colored versions:

The maintainers will now check for:

1. The number of Glyphs matches the number of SVGs that were selected.
2. The icons (second group of pictures) look the same as the SVGs (first group of pictures).
3. The icons are of high quality (legible, matches the official logo, etc.)

In case of font issues, it might be caused by Icomoon not accepting strokes in the SVGs. Check this doc for more details and fix the issues as instructed by Icomoon and update this PR once you are done.

Thank you for contributing to Devicon! I hope that your icons are accepted into the repository.

Note: If the images don't show up, it has been autodeleted by Imgur after 6 months due to our API choice.

Cheers,
Peek Bot 😊

[Panquesito7]

LGTM 🚀 Thank you for your contribution! 😄👍