chore(package): update html-webpack-plugin to version 4.2.0

Closes #116

Author: greenkeeper[bot]

package.json

@@ -44,7 +44,7 @@
     "extract-text-webpack-plugin": "^4.0.0-beta.0",
     "file-loader": "^5.0.2",
     "html-loader": "^0.5.5",
-    "html-webpack-plugin": "^3.2.0",
+    "html-webpack-plugin": "^4.2.0",
     "http-server": "^0.12.1",
     "istanbul-instrumenter-loader": "^3.0.1",
     "jasmine-core": "^3.5.0",