chore(package): update cssnano to version 4.1.2

Closes #430

Author: greenkeeper[bot]

package.json

@@ -98,7 +98,7 @@
     "codelyzer": "3.2.1",
     "compression-webpack-plugin": "1.0.1",
     "css-loader": "0.28.7",
-    "cssnano": "4.0.0-rc.2",
+    "cssnano": "4.1.2",
     "exports-loader": "0.6.4",
     "extract-text-webpack-plugin": "3.0.1",
     "favicons-webpack-plugin": "0.0.7",