chore(package): update cssnano to version 4.1.0

Closes #7

Author: greenkeeper[bot]

package.json

@@ -28,7 +28,7 @@
   "author": "Brian Sipple <@Brian_Sipple>",
   "license": "MIT",
   "devDependencies": {
-    "cssnano": "^3.9.1",
+    "cssnano": "^4.1.0",
     "del-cli": "^0.2.1",
     "http-server": "^0.9.0",
     "npmpub": "^3.1.0",