chore(package): update postcss-loader to version 3.0.0

package.json

@@ -71,7 +71,7 @@
     "minilog": "3.1.0",
     "mkdirp": "^0.5.1",
     "postcss-import": "^11.0.0",
-    "postcss-loader": "^2.1.4",
+    "postcss-loader": "^3.0.0",
     "postcss-simple-vars": "^4.0.0",
     "prop-types": "^15.5.10",
     "raf": "^3.4.0",