Bump core-js from 3.8.3 to 3.9.1 in /swift_browser_ui_frontend

Bumps [core-js](https://github.com/zloirock/core-js/tree/HEAD/packages/core-js) from 3.8.3 to 3.9.1.
- [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>

swift_browser_ui_frontend/package.json

@@ -12,7 +12,7 @@
   "dependencies": {
     "@vue/cli-service-global": "^4.5.11",
     "buefy": "^0.9.4",
-    "core-js": "^3.8.3",
+    "core-js": "^3.9.1",
     "lodash": "^4.17.20",
     "material-design-icons": "^3.0.1",
     "node-sass": "^4.14.1",