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

@@ -10,7 +10,7 @@
     "url": "https://github.com/textpattern/textpattern-com-website/issues"
   },
   "devDependencies": {
-    "autoprefixer": "9.8.5",
+    "autoprefixer": "9.8.6",
     "cssnano": "4.1.10",
     "grunt": "1.2.1",
     "grunt-cli": "1.3.2",