fix(package): update core-js to version 3.1.4 (#488)

Author: greenkeeper[bot]

package.json

@@ -56,7 +56,7 @@
     "chalk": "^2.4.1",
     "compatible-debug": "^1.0.0",
     "cookie-parser": "^1.4.4",
-    "core-js": "3.0.1",
+    "core-js": "3.1.4",
     "draft-js": "^0.10.5",
     "draft-js-linkify-plugin": "^2.0.1",
     "draft-js-mention-plugin": "3.1.3",