Bump uglifyjs-webpack-plugin from 1.2.2 to 1.2.4

Bumps [uglifyjs-webpack-plugin](https://github.com/webpack-contrib/uglifyjs-webpack-plugin) from 1.2.2 to 1.2.4.
- [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](webpack-contrib/uglifyjs-webpack-plugin@v1.2.2...v1.2.4)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot-support