fix(package): update core-js to version 3.1.1

Closes #350

Author: greenkeeper[bot]

package.json

@@ -44,7 +44,7 @@
     "@types/lodash": "4.14.130",
     "@types/shelljs": "0.8.4",
     "angular-tree-component": "7.2.0",
-    "core-js": "2.6.4",
+    "core-js": "3.1.1",
     "electron": "1.7.12",
     "electron-settings": "3.1.4",
     "lodash": "4.17.11",