Removes [webpack-dev-middleware](https://github.com/webpack/webpack-dev-middleware). It's no longer used after updating ancestor dependency [@microsoft/sp-build-web](http://aka.ms/spfx). These dependencies need to be updated together.
Removes `webpack-dev-middleware`
Updates `@microsoft/sp-build-web` from 1.15.2 to 1.20.1
---
updated-dependencies:
- dependency-name: webpack-dev-middleware
dependency-type: indirect
- dependency-name: "@microsoft/sp-build-web"
dependency-type: direct:development
...
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dependabot[bot]
Dan Toft