chore: referencing this dependency from NPM

as github might be inaccessible / blocked on some environments (for whatever/security reasons), it's probably better to reference this dependency from NPM instead of Github as well, and solve the problem of referencing to the beta version by its exact upper version number.

Author: mfranzke

packages/uikit-workshop/package.json

@@ -91,7 +91,7 @@
     "hogan.js": "^3.0.2",
     "htm": "^1.0.1",
     "html-loader": "^0.5.5",
-    "html-webpack-plugin": "github:jantimon/html-webpack-plugin#webpack-4",
+    "html-webpack-plugin": "^4.0.0-beta.11",
     "iframe-resizer": "^3.6.5",
     "lit-element": "^2.2.1",
     "lit-html": "^1.1.2",