Update dependency html-webpack-plugin to v4.0.0-beta.7

Author: renovate-bot

playground/package-lock.json

@@ -32,7 +32,7 @@
     "handlebars-loader": "1.7.0",
     "html-loader": "0.5.5",
     "html-webpack-inline-source-plugin": "1.0.0-beta.2",
-    "html-webpack-plugin": "4.0.0-beta.5",
+    "html-webpack-plugin": "4.0.0-beta.7",
     "js-beautify": "1.8.6",
     "keymaster": "1.6.2",
     "mini-css-extract-plugin": "0.5.0",