chore(package): update extract-text-webpack-plugin to version 3.0.2

Closes #108

Author: greenkeeper[bot]

package.json

@@ -47,7 +47,7 @@
     "eslint": "^4.2.0",
     "eslint-loader": "^1.9.0",
     "eslint-plugin-react": "^7.1.0",
-    "extract-text-webpack-plugin": "^2.1.2",
+    "extract-text-webpack-plugin": "^3.0.2",
     "file-loader": "^0.11.2",
     "html-webpack-plugin": "^2.29.0",
     "json-loader": "^0.5.4",