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

Closes #37

Author: greenkeeper[bot]

package.json

@@ -62,7 +62,7 @@
         "es6-map": "^0.1.5",
         "es6-symbol": "^3.1.1",
         "glslify": "^7.0.0",
-        "html-webpack-plugin": "^3.2.0",
+        "html-webpack-plugin": "^4.2.0",
         "imports-loader": "^0.8.0",
         "istanbul": "^0.4.5",
         "istanbul-instrumenter-loader": "^3.0.1",