Bump core-js from 2.6.12 to 3.9.1

Bumps [core-js](https://github.com/zloirock/core-js/tree/HEAD/packages/core-js) from 2.6.12 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>

package.json

@@ -26,7 +26,7 @@
     "@types/heatmap.js": "^2.0.36",
     "ajv": "^7.2.1",
     "bootstrap": "^4.6.0",
-    "core-js": "^2.6.12",
+    "core-js": "^3.9.1",
     "heatmap.js": "^2.0.5",
     "jquery": "^3.6.0",
     "leaflet": "^1.7.1",