chore(package): update core-js to version 3.4.8

Closes #42

Author: greenkeeper[bot]

package.json

@@ -65,7 +65,7 @@
     "commitplease": "^3.2.0",
     "conventional-github-releaser": "^2.0.2",
     "copy-webpack-plugin": "^5.0.2",
-    "core-js": "^2.6.5",
+    "core-js": "^3.4.8",
     "css-loader": "^1.0.1",
     "cssnano": "^4.1.10",
     "del": "^3.0.0",