Update dependency pixi.js to v8 (#29)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| pixi.js | [`^7.1.2` ->
`^8.0.0`](https://renovatebot.com/diffs/npm/pixi.js/7.4.2/8.0.3) |
[![age](https://developer.mend.io/api/mc/badges/age/npm/pixi.js/8.0.3?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/npm/pixi.js/8.0.3?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/npm/pixi.js/7.4.2/8.0.3?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/pixi.js/7.4.2/8.0.3?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

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