Bump webpack-dev-server from 3.11.3 to 5.2.1 in /example (#571)

Bumps [webpack-dev-server](https://github.com/webpack/webpack-dev-server) from 3.11.3 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@v3.11.3...v5.2.1)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

example/package.json

@@ -32,7 +32,7 @@
     "rescript": "11.0.0-rc.8",
     "webpack": "^4.41.2",
     "webpack-cli": "^3.3.9",
-    "webpack-dev-server": "^3.9.0"
+    "webpack-dev-server": "^5.2.1"
   },
   "author": "bootstrapdash",
   "url": "http://www.bootstrapdash.com/",