Bump core-js from 3.14.0 to 3.15.0 in /frontend

Bumps [core-js](https://github.com/zloirock/core-js/tree/HEAD/packages/core-js) from 3.14.0 to 3.15.0.
- [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/v3.15.0/packages/core-js)

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

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

frontend/package.json

@@ -8,7 +8,7 @@
     "lint": "vue-cli-service lint"
   },
   "dependencies": {
-    "core-js": "^3.14.0",
+    "core-js": "^3.15.0",
     "pretty-checkbox-vue": "^1.1.9",
     "register-service-worker": "^1.7.2",
     "socket.io-client": "^4.1.2",

frontend/yarn.lock

@@ -2929,10 +2929,10 @@ core-js@^2.4.0:
   resolved "https://registry.npm.taobao.org/core-js/download/core-js-2.6.12.tgz?cache=0&sync_timestamp=1606326948512&other_urls=https%3A%2F%2Fregistry.npm.taobao.org%2Fcore-js%2Fdownload%2Fcore-js-2.6.12.tgz#d9333dfa7b065e347cc5682219d6f690859cc2ec"
   integrity sha1-2TM9+nsGXjR8xWgiGdb2kIWcwuw=
 
-core-js@^3.14.0, core-js@^3.6.5:
-  version "3.14.0"
-  resolved "https://registry.yarnpkg.com/core-js/-/core-js-3.14.0.tgz#62322b98c71cc2018b027971a69419e2425c2a6c"
-  integrity sha512-3s+ed8er9ahK+zJpp9ZtuVcDoFzHNiZsPbNAAE4KXgrRHbjSqqNN6xGSXq6bq7TZIbKj4NLrLb6bJ5i+vSVjHA==
+core-js@^3.15.0, core-js@^3.6.5:
+  version "3.15.0"
+  resolved "https://registry.yarnpkg.com/core-js/-/core-js-3.15.0.tgz#db9554ebce0b6fd90dc9b1f2465c841d2d055044"
+  integrity sha512-GUbtPllXMYRzIgHNZ4dTYTcUemls2cni83Q4Q/TrFONHfhcg9oEGOtaGHfb0cpzec60P96UKPvMkjX1jET8rUw==
 
 core-util-is@1.0.2, core-util-is@~1.0.0:
   version "1.0.2"