fix(package): update extract-text-webpack-plugin to version 3.0.0

Closes #38

Author: greenkeeper[bot]

package.json

@@ -37,7 +37,7 @@
     "cross-env": "^3.1.3",
     "css-loader": "0.25.0",
     "express": "4.14.0",
-    "extract-text-webpack-plugin": "1.0.1",
+    "extract-text-webpack-plugin": "3.0.0",
     "findup": "0.1.5",
     "glob": "7.1.1",
     "lodash": "4.16.6",