chore(package): update html-webpack-plugin to version 4.0.4

Closes #151

Author: greenkeeper[bot]

package.json

@@ -91,7 +91,7 @@
     "express": "^4.15.3",
     "extract-text-webpack-plugin": "^4.0.0-beta.0",
     "file-loader": "^2.0.0",
-    "html-webpack-plugin": "^3.2.0",
+    "html-webpack-plugin": "^4.0.4",
     "identity-obj-proxy": "^3.0.0",
     "jest": "^22.4.2",
     "jsdom": "^11.0.0",