chore(deps): update core-js requirement

Updates the requirements on [core-js](https://github.com/zloirock/core-js/tree/HEAD/packages/core-js) to permit the latest version.
- [Release notes](https://github.com/zloirock/core-js/releases)
- [Changelog](https://github.com/zloirock/core-js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/zloirock/core-js/commits/v3.9.1/packages/core-js)

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

packages/generator/app/templates/package.json

@@ -31,7 +31,7 @@
     "babel-loader": "^8.2.2",
     "classnames": "^2.2.6",
     "copy-webpack-plugin": "^6.4.1",
-    "core-js": "^3.8.1",
+    "core-js": "^3.9.1",
     "css-loader": "^5.1.3",
     "html-webpack-plugin": "^4.5.2",
     "postcss-import": "^14.0.0",