Bump postcss from 7.0.18 to 8.2.10

Bumps [postcss](https://github.com/postcss/postcss) from 7.0.18 to 8.2.10.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@7.0.18...8.2.10)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

package-lock.json

@@ -44,7 +44,7 @@
     "mocha": "^6.2.3",
     "node-sass": "^4.14.1",
     "npm-run-all": "^4.1.5",
-    "postcss": "^7.0.18",
+    "postcss": "^8.2.10",
     "rollup": "^1.12.0",
     "rollup-plugin-commonjs": "^10.0.0",
     "rollup-plugin-livereload": "^1.0.0",