chore: upgrade core-js from 2.6.5 to 2.6.9

Snyk has created this PR to upgrade core-js from 2.6.5 to 2.6.9.

See this package in NPM:
https://www.npmjs.com/package/core-js

See this project in Snyk:
https://app.snyk.io/org/thislooksfun/project/bae0dfd4-a180-44c2-8aa2-3d8c2f9014e1?utm_source=github&utm_medium=upgrade-pr

package.json

@@ -23,7 +23,7 @@
   "dependencies": {
     "bootstrap": "^4.3.1",
     "bootstrap-vue": "^2.0.0-rc.28",
-    "core-js": "^2.6.5",
+    "core-js": "^2.6.9",
     "electron-config": "^2.0.0",
     "electron-window-state": "^5.0.3",
     "js-yaml-loader": "^1.2.2",