Bump core-js from 2.6.5 to 3.40.0

Bumps [core-js](https://github.com/zloirock/core-js/tree/HEAD/packages/core-js) from 2.6.5 to 3.40.0.
- [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/v3.40.0/packages/core-js)

---
updated-dependencies:
- dependency-name: core-js
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

package.json

@@ -43,7 +43,7 @@
     "bulma": "^0.9.4",
     "bulma-extensions": "^6.2.7",
     "bulmaswatch": "^0.8.1",
-    "core-js": "^2.5.4",
+    "core-js": "^3.40.0",
     "dompurify": "^3.2.3",
     "flag-icon-css": "^4.1.7",
     "lodash": "^4.17.15",