chore(deps): update dependency autoprefixer to v10.4.20 (#298)

This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [autoprefixer](https://redirect.github.com/postcss/autoprefixer) |
[`10.4.14` ->
`10.4.20`](https://renovatebot.com/diffs/npm/autoprefixer/10.4.14/10.4.20)
|
[![age](https://developer.mend.io/api/mc/badges/age/npm/autoprefixer/10.4.20?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/npm/autoprefixer/10.4.20?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/npm/autoprefixer/10.4.14/10.4.20?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/autoprefixer/10.4.14/10.4.20?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

### Release Notes

<details>
<summary>postcss/autoprefixer (autoprefixer)</summary>

###
[`v10.4.20`](https://redirect.github.com/postcss/autoprefixer/blob/HEAD/CHANGELOG.md#10420)

[Compare
Source](https://redirect.github.com/postcss/autoprefixer/compare/10.4.19...10.4.20)

-   Fixed `fit-content` prefix for Firefox.

###
[`v10.4.19`](https://redirect.github.com/postcss/autoprefixer/blob/HEAD/CHANGELOG.md#10419)

[Compare
Source](https://redirect.github.com/postcss/autoprefixer/compare/10.4.18...10.4.19)

- Removed `end value has mixed support, consider using flex-end` warning
    since `end`/`start` now have good support.

###
[`v10.4.18`](https://redirect.github.com/postcss/autoprefixer/blob/HEAD/CHANGELOG.md#10418)

[Compare
Source](https://redirect.github.com/postcss/autoprefixer/compare/10.4.17...10.4.18)

- Fixed removing `-webkit-box-orient` on `-webkit-line-clamp`
([@&#8203;Goodwine](https://redirect.github.com/Goodwine)).

###
[`v10.4.17`](https://redirect.github.com/postcss/autoprefixer/blob/HEAD/CHANGELOG.md#10417)

[Compare
Source](https://redirect.github.com/postcss/autoprefixer/compare/10.4.16...10.4.17)

-   Fixed `user-select: contain` prefixes.

###
[`v10.4.16`](https://redirect.github.com/postcss/autoprefixer/blob/HEAD/CHANGELOG.md#10416)

[Compare
Source](https://redirect.github.com/postcss/autoprefixer/compare/10.4.15...10.4.16)

-   Improved performance (by Romain Menke).
-   Fixed docs (by Christian Oliff).

###
[`v10.4.15`](https://redirect.github.com/postcss/autoprefixer/blob/HEAD/CHANGELOG.md#10415)

[Compare
Source](https://redirect.github.com/postcss/autoprefixer/compare/10.4.14...10.4.15)

-   Fixed `::backdrop` prefixes (by 一丝).
-   Fixed docs (by Christian Oliff).

</details>

---

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---

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