Bump purgecss-webpack-plugin from 0.23.0 to 1.1.0

Bumps [purgecss-webpack-plugin](https://github.com/FullHuman/purgecss) from 0.23.0 to 1.1.0.
- [Release notes](https://github.com/FullHuman/purgecss/releases)
- [Changelog](https://github.com/FullHuman/purgecss/blob/master/CHANGELOG.md)
- [Commits](https://github.com/FullHuman/purgecss/commits/1.1.0)

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

package.json

@@ -66,7 +66,7 @@
     "preact-router": "^3.2.1",
     "preact-svg-loader": "^0.2.1",
     "promise-polyfill": "^8.1.3",
-    "purgecss-webpack-plugin": "0.23.0",
+    "purgecss-webpack-plugin": "1.1.0",
     "regenerator-runtime": "^0.13.3",
     "supertest": "^4.0.2",
     "unfetch": "^4.1.0"