Bump webpack-dev-server from 2.4.5 to 3.1.11 in /examples/tree-shaking

Bumps [webpack-dev-server](https://github.com/webpack/webpack-dev-server) from 2.4.5 to 3.1.11.
- [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@v2.4.5...v3.1.11)

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

examples/tree-shaking/package.json

@@ -26,6 +26,6 @@
     "uglify-js-harmony": "^2.7.5",
     "webpack": "^2.4.0",
     "webpack-bundle-analyzer": "^2.4.0",
-    "webpack-dev-server": "^2.4.0"
+    "webpack-dev-server": "^3.1.11"
   }
 }