chore(package): update postcss-nested to version 4.1.0

Closes #20

Author: greenkeeper[bot]

package.json

@@ -32,7 +32,7 @@
     "extract-text-webpack-plugin": "^3.0.0",
     "postcss-cssnext": "^3.0.2",
     "postcss-loader": "^2.0.6",
-    "postcss-nested": "^3.0.0",
+    "postcss-nested": "^4.1.0",
     "raw-loader": "^0.5.1",
     "react-dom": "^15.6.1",
     "storybook-readme": "^3.0.5",