chore(package): update html-webpack-plugin to version 4.0.1

Closes #157

Author: greenkeeper[bot]

package.json

@@ -76,7 +76,7 @@
     "eslint-plugin-standard": "^4.0.0",
     "file-loader": "^3.0.1",
     "flow-bin": "0.91.0",
-    "html-webpack-plugin": "^3.2.0",
+    "html-webpack-plugin": "^4.0.1",
     "jest": "23.6.0",
     "json-loader": "^0.5.4",
     "node-sass": "4.11.0",