Bump terser and terser-webpack-plugin

Bumps [terser](https://github.com/terser/terser) and [terser-webpack-plugin](https://github.com/webpack-contrib/terser-webpack-plugin). These dependencies needed to be updated together.

Updates `terser` from 3.16.1 to 4.8.1
- [Release notes](https://github.com/terser/terser/releases)
- [Changelog](https://github.com/terser/terser/blob/master/CHANGELOG.md)
- [Commits](terser/terser@v3.16.1...v4.8.1)

Updates `terser-webpack-plugin` from 1.2.2 to 1.4.5
- [Release notes](https://github.com/webpack-contrib/terser-webpack-plugin/releases)
- [Changelog](https://github.com/webpack-contrib/terser-webpack-plugin/blob/v1.4.5/CHANGELOG.md)
- [Commits](webpack/terser-webpack-plugin@v1.2.2...v1.4.5)

---
updated-dependencies:
- dependency-name: terser
  dependency-type: indirect
- dependency-name: terser-webpack-plugin
  dependency-type: indirect
...

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Author: dependabot[bot]