npm: Update to PostCSS 8

package.json

@@ -99,8 +99,9 @@
     "ora": "3.4.0",
     "path-to-regexp": "2.4.0",
     "portfinder": "1.0.32",
-    "postcss-loader": "2.1.6",
-    "postcss-url": "7.3.2",
+    "postcss": "8.4.16",
+    "postcss-loader": "4.0.3",
+    "postcss-url": "10.1.3",
     "rimraf": "2.7.1",
     "sass-loader": "7.3.1",
     "script-loader": "0.7.2",