fix(package): update core-js to version 3.5.0

Closes #22

Author: greenkeeper[bot]

package.json

@@ -110,7 +110,7 @@
     "validate-commit-msg": "^2.12.2"
   },
   "dependencies": {
-    "core-js": "^2.5.7",
+    "core-js": "^3.5.0",
     "jest": "^23.2.0"
   }
 }