chore(package): update core-js to version 3.3.3

Closes #137

Author: greenkeeper[bot]

package.json

@@ -81,7 +81,7 @@
     "browserstack-local": "^1.4.0",
     "codelyzer": "4.5.0",
     "commitizen": "^3.0.0",
-    "core-js": "^2.4.1",
+    "core-js": "^3.3.3",
     "coveralls": "^3.0.0",
     "cz-conventional-changelog": "^2.0.0",
     "glob": "^7.1.3",