chore: release v0.1.6

Bumps [postcss-preset-env](https://github.com/csstools/postcss-plugins/tree/HEAD/plugin-packs/postcss-preset-env) from 8.2.0 to 8.3.0.
- [Release notes](https://github.com/csstools/postcss-plugins/releases)
- [Changelog](https://github.com/csstools/postcss-plugins/blob/main/plugin-packs/postcss-preset-env/CHANGELOG.md)
- [Commits](https://github.com/csstools/postcss-plugins/commits/HEAD/plugin-packs/postcss-preset-env)

---
updated-dependencies:
- dependency-name: postcss-preset-env
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "x-markdown-css",
-  "version": "0.1.5",
+  "version": "0.1.6",
   "description": "A simple and customizable markdown CSS stylesheet for everyone.",
   "keywords": [
     "markdown",
@@ -51,7 +51,7 @@
     "@lodder/grunt-postcss": "^3.1.1",
     "autoprefixer": "^10.4.13",
     "bumpp": "^9.0.0",
-    "cssnano": "^5.1.15",
+    "cssnano": "^6.0.0",
     "grunt": "^1.6.1",
     "grunt-sass": "^3.1.0",
     "load-grunt-tasks": "^5.1.0",