Bump core-js from 3.4.8 to 3.6.4

Bumps [core-js](https://github.com/zloirock/core-js) from 3.4.8 to 3.6.4.
- [Release notes](https://github.com/zloirock/core-js/releases)
- [Changelog](https://github.com/zloirock/core-js/blob/master/CHANGELOG.md)
- [Commits](zloirock/core-js@v3.4.8...v3.6.4)

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

package.json

@@ -9,7 +9,7 @@
   },
   "dependencies": {
     "bootstrap-vue": "^2.3.0",
-    "core-js": "^3.4.8",
+    "core-js": "^3.6.4",
     "firebase": "^7.7.0",
     "vue": "^2.6.10",
     "vue-chat-scroll": "^1.3.6",