Bump uglifyjs-webpack-plugin from 2.1.3 to 2.2.0 in /js

Bumps [uglifyjs-webpack-plugin](https://github.com/webpack-contrib/uglifyjs-webpack-plugin) from 2.1.3 to 2.2.0.
- [Release notes](https://github.com/webpack-contrib/uglifyjs-webpack-plugin/releases)
- [Changelog](https://github.com/webpack-contrib/uglifyjs-webpack-plugin/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack-contrib/uglifyjs-webpack-plugin/compare/v2.1.3...v2.2.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

js/package.json

@@ -35,7 +35,7 @@
     "karma": "^4.2.0",
     "mini-css-extract-plugin": "^0.8.0",
     "style-loader": "^0.23.1",
-    "uglifyjs-webpack-plugin": "^2.1.3",
+    "uglifyjs-webpack-plugin": "^2.2.0",
     "url-loader": "^2.1.0",
     "vue-loader": "^15.7.1",
     "vue-style-loader": "^4.1.2",