Bump nodemailer from 6.4.6 to 6.4.16 in /20. File Upload and Download

Bumps [nodemailer](https://github.com/nodemailer/nodemailer) from 6.4.6 to 6.4.16.
- [Release notes](https://github.com/nodemailer/nodemailer/releases)
- [Changelog](https://github.com/nodemailer/nodemailer/blob/master/CHANGELOG.md)
- [Commits](nodemailer/nodemailer@v6.4.6...v6.4.16)

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

Author: dependabot[bot]

20. File Upload and Download/package-lock.json

@@ -38,7 +38,7 @@
     "mongodb": "^3.5.5",
     "mongoose": "^5.9.6",
     "multer": "^1.4.2",
-    "nodemailer": "^6.4.6",
+    "nodemailer": "^6.4.16",
     "pdfkit": "^0.11.0"
   },
   "devDependencies": {