Bump serialize-javascript and terser-webpack-plugin in /s2018

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

Updates `serialize-javascript` from 2.1.2 to 4.0.0
- [Release notes](https://github.com/yahoo/serialize-javascript/releases)
- [Commits](yahoo/serialize-javascript@v2.1.2...v4.0.0)

Updates `terser-webpack-plugin` from 1.4.3 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@v1.4.3...v1.4.5)

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

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Author: dependabot[bot]