chore(package): update postcss to version 7.0.23

Closes #348

Author: greenkeeper[bot]

package.json

@@ -52,7 +52,7 @@
     "html-webpack-plugin": "3.2.0",
     "http-server": "0.11.1",
     "lighthouse": "4.1.0",
-    "postcss": "7.0.14",
+    "postcss": "7.0.23",
     "postcss-cssnext": "3.1.0",
     "postcss-custom-media": "7.0.7",
     "postcss-discard-comments": "4.0.1",