fixed issue with babel plugin proposal class properties that initiated

properties to void 0. This breaks angularjs preAssignBinding which
applies bindings to this before constructor is called. Fixed by
using fork of babel plugin.

https://github.com/babel/babel/issues/8417

scripts/webpack/webpack.hot.js

@@ -55,7 +55,7 @@ module.exports = merge(common, {
             cacheDirectory: true,
             babelrc: false,
             plugins: [
-              ["@babel/plugin-proposal-class-properties", { loose: true }],
+              [require("@rtsao/plugin-proposal-class-properties"), { loose: true }],
               'angularjs-annotate',
               'syntax-dynamic-import', // needed for `() => import()` in routes.ts
               'react-hot-loader/babel'