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

[dariakiseleva]

Double check these details before you open a PR

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

This PR closes NONE

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

https://pixijs.com/branding

[dariakiseleva]

Thank you for reviewing and spotting these errors! I have now adjusted the files.