fix regressions from webpack-contrib/uglifyjs-webpack-plugin#174

lib/builder/webpack/client.config.js

@@ -142,6 +142,11 @@ export default function webpackClientConfig() {
         sourceMap: true,
         extractComments: {
           filename: 'LICENSES'
+        },
+        uglifyOptions: {
+          output: {
+            comments: /^\**!|@preserve|@license|@cc_on/
+          }
         }
       })
     )