Bump helmet from 3.23.3 to 4.0.0

Bumps [helmet](https://github.com/helmetjs/helmet) from 3.23.3 to 4.0.0.
- [Release notes](https://github.com/helmetjs/helmet/releases)
- [Changelog](https://github.com/helmetjs/helmet/blob/master/CHANGELOG.md)
- [Commits](https://github.com/helmetjs/helmet/compare/v3.23.3...v4.0.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -9,7 +9,7 @@
     "express": "^4.16.4",
     "formidable": "^1.2.1",
     "fs-extra": "^9.0.0",
-    "helmet": "^3.15.1",
+    "helmet": "^4.0.0",
     "lowdb": "^1.0.0",
     "path": "^0.12.7",
     "remarkable": "^2.0.0",