FE-2501 broken build script

[ian-forster]

Description

This PR fixes v11.0.0 by replacing the asset object with a filename object in webpack.config.js as per the release notes for compression-webpack-plugin v2.0.0.
https://github.com/webpack-contrib/compression-webpack-plugin/releases/tag/v2.0.0

Currently v11.0.0 causes broken builds because the asset object is no longer part of the compression-webpack-plugin API.

Checklist

• CHANGELOG.md update
• Package.json version bump

Additional context

N/A

Testing instructions

You need to prepare a clean file system to test that the new files are installed and that any previous build is discarded.

1. I've built a test branch of Carbon that includes this branch of carbon-factory, it's available here: FE-2501-test-branch
2. Check it out and ensure your deploy/ directory only has files from the repo, Ie. index.html, favicon.ico & images/ directory
3. $ npm install
4. $ npm run-script build

This should build and populate deploy/assets/ deploy/docs/ and deploy/storybook/ and not throw any Errors.