Update dependency cron to v4

Author: renovate[bot]

package-lock.json

@@ -34,7 +34,7 @@
     "babel-eslint": "^10.0.1",
     "babel-loader": "^8.0.5",
     "body-parser": "^1.18.3",
-    "cron": "^1.7.1",
+    "cron": "^4.0.0",
     "cross-env": "^5.2.1",
     "css-loader": "^2.1.0",
     "date-fns": "^2.14.0",