Bump webpack-dev-server from 2.2.0 to 5.2.1 in /www

Bumps [webpack-dev-server](https://github.com/webpack/webpack-dev-server) from 2.2.0 to 5.2.1.
- [Release notes](https://github.com/webpack/webpack-dev-server/releases)
- [Changelog](https://github.com/webpack/webpack-dev-server/blob/master/CHANGELOG.md)
- [Commits](webpack/webpack-dev-server@v2.2.0...v5.2.1)

---
updated-dependencies:
- dependency-name: webpack-dev-server
  dependency-version: 5.2.1
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

www/package.json

@@ -76,6 +76,6 @@
     "style-loader": "^0.13.1",
     "url-loader": "^0.5.9",
     "webpack": "3.5.0",
-    "webpack-dev-server": "2.2.0"
+    "webpack-dev-server": "5.2.1"
   }
 }