Bump autoprefixer from 9.8.5 to 9.8.6

Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 9.8.5 to 9.8.6.
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/master/CHANGELOG.md)
- [Commits](postcss/autoprefixer@9.8.5...9.8.6)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

package.json

@@ -25,7 +25,7 @@
     "url": "https://github.com/textpattern/textpattern-default-theme/issues"
   },
   "devDependencies": {
-    "autoprefixer": "9.8.5",
+    "autoprefixer": "9.8.6",
     "clean-webpack-plugin": "3.0.0",
     "copy-webpack-plugin": "6.0.3",
     "cross-env": "7.0.2",