chore(package): update css-loader to version 3.1.0

Closes #9

Author: greenkeeper[bot]

package.json

@@ -27,7 +27,7 @@
   },
   "devDependencies": {
     "clean-webpack-plugin": "^1.0.0",
-    "css-loader": "^2.0.0",
+    "css-loader": "^3.1.0",
     "file-loader": "^3.0.0",
     "html-webpack-inline-source-plugin": "0.0.10",
     "html-webpack-plugin": "^3.2.0",