Merge pull request #697 from opensheetmusicdisplay/greenkeeper/html-webpack-plugin-4.0.0

Update html-webpack-plugin to the latest version 🚀

package.json

@@ -86,7 +86,7 @@
     "eslint-plugin-node": "^11.0.0",
     "eslint-plugin-promise": "^4.2.1",
     "eslint-plugin-standard": "^4.0.0",
-    "html-webpack-plugin": "^3.2.0",
+    "html-webpack-plugin": "^4.0.0",
     "jquery": "^3.4.1",
     "jsdom": "^16.2.0",
     "karma": "^4.1.0",