fix: use `cause` to keep original errors and warnings

[alexander-akait]

This PR contains a:

• [x] bugfix
• [ ] new feature
• [ ] code refactor
• [ ] test update
• [ ] typo fix
• [x] metadata update

Motivation / Use-Case

use cause to keep original error

Breaking Changes

No

Additional Info

I am preparing good error reporting for CSS in webpack

[codecov[bot]]

Codecov Report

Patch coverage: 95.45% and no project coverage change.

Comparison is base (7e5eaeb) 88.76% compared to head (6076fd5) 88.76%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #655 +/- ## ======================================= Coverage 88.76% 88.76% ======================================= Files 3 3 Lines 356 356 Branches 115 115 ======================================= Hits 316 316 Misses 37 37 Partials 3 3 ``` | [Impacted Files](https://app.codecov.io/gh/webpack-contrib/postcss-loader/pull/655?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=webpack-contrib) | Coverage Δ | | |---|---|---| | [src/utils.js](https://app.codecov.io/gh/webpack-contrib/postcss-loader/pull/655?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=webpack-contrib#diff-c3JjL3V0aWxzLmpz) | `86.51% <95.45%> (ø)` | |

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